Reduced radius optical fiber with high mechanical reliability

ABSTRACT

The present disclosure provides optical fibers with an impact-resistant coating system. The fibers feature low microbending and high mechanical reliability. The coating system includes a primary coating and a secondary coating. The primary coating and secondary coating have reduced thickness to provide reduced radius fibers without sacrificing protection. The primary coating has a low spring constant and sufficient thickness to resist transmission of force to the glass fiber. The secondary coating has high puncture resistance. The outer diameter of the optical fiber is less than or equal to 200 μm.

This application claims the benefit of priority to Dutch PatentApplication No. 2024737 filed on Jan. 23, 2020, which claims priorityfrom U.S. Provisional Patent Application Ser. No. 62/957,879 filed onJan. 7, 2020, the content of which is relied upon and incorporatedherein by reference in its entirety.

FIELD OF THE DISCLOSURE

This disclosure pertains to optical fibers and assemblies of opticalfibers. More particularly, this disclosure pertains to optical fibersand optical fiber cables configured for submarine environments. Mostparticularly, this disclosure pertains to optical fibers having reduceddiameters and optical fiber cables having a high number of opticalfibers.

BACKGROUND OF THE DISCLOSURE

Optical fibers with reduced diameters are attractive for reducing thesize of ribbons and cables needed to accommodate a given optical fibercount, increasing the optical fiber count of ribbons of a given lengthor cables of a given diameter, decreasing ribbon or cable cost,efficiently using existing infrastructure for upgrading ribbon or cableinstallations, and reducing the footprint of new ribbon or cableinstallations.

In particular, there is an increasing demand for submarine optical fibertransmission capacity driven by the rapid growth of internet trafficamong different continents. To increase the transmission capacity,wavelength division multiplexing has been used to increase the number oftransmission channels and advanced modulation formats have beendeveloped to increase the data rate per channel. However, the number ofchannels and channel data rate are nearly at the practical limits andincreasing the number of fibers is unavoidable.

A submarine cable is designed to protect the fibers inside from waterdamage and other mechanical damages. The size of deep-sea cable istypically around 17-20 mm in diameter for easy installation and lessvulnerability. Therefore, the space for optical fibers is limited and itis desirable to increase the fiber count without increasing the cablesize.

There is accordingly a need for optical fibers having reduced diameterto increase the fiber count in cables of fixed size. In particular,there is a need for optical fibers having reduced glass diameter and/orreduced coating thickness that provide the performance needed for longhaul transmission in submarine environments.

SUMMARY

The present disclosure provides low diameter optical fibers with animpact-resistant coating system and low microbend loss. The opticalfiber includes a glass fiber with a radius less than the standard radius(62.5 μm) used in the industry. The coating system includes a primarycoating and a secondary coating. The modulus and thickness of thesecondary coating are configured to provide puncture resistance. Theprimary coating functions in conjunction with the secondary coating tominimize microbend losses. The primary coating also has high tearstrength and is resistant to damage caused by thermal and mechanicalstresses that arise during the fiber manufacturing process. The radiusof the glass fiber and combined thicknesses of the primary and secondarycoatings are configured to provide an optical fiber with an outer radiusof less than or equal to 100 μm.

The present description extends to:

An optical fiber comprising:

a core region, the core region comprising silica glass doped with analkali metal oxide, the core region having a radius r₁ in the range from3.0 μm to 10.0 μm and a relative refractive index profile Δ₁ having amaximum relative refractive index Δ_(1max) in the range from −0.15% to0.30%;

a cladding region surrounding and directly adjacent to the core region,the cladding region having a radius r₄ in the range from 37.5 μm to 52.5μm;

a primary coating surrounding and directly adjacent to the claddingregion, the primary coating having a radius r₅, a spring constant χ_(p),an in situ modulus in the range from 0.05 MPa to 0.30 MPa and athickness r₅−r₄ in the range from 20.0 μm to 40.0 μm; and

a secondary coating surrounding and directly adjacent to the primarycoating, the secondary coating having a radius r₆ less than or equal to100.0 μm, a Young's modulus greater than 1600 MPa and a thickness r₆−r₅in the range from 15.0 μm to 30.0 μm.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understand the natureand character of the claims.

The accompanying drawings are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings are illustrative of selected aspects of thepresent disclosure, and together with the description serve to explainprinciples and operation of methods, products, and compositions embracedby the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a coated optical fiber according oneembodiment.

FIG. 2 is a schematic view of a representative optical fiber ribbon.

FIG. 3 is a schematic view of a representative optical fiber cable.

FIG. 4A depicts a cross-sectional view of an optical fiber having a coreregion, an inner cladding region, an intermediate cladding region, anouter cladding region, a primary coating, and a secondary coating.

FIG. 4B depicts a cross-sectional view of an optical fiber having a coreregion, an intermediate cladding region, an outer cladding region, aprimary coating, and a secondary coating.

FIG. 5A depicts a relative refractive index profile of a glass fiberhaving a core region, an inner cladding region, an intermediate claddingregion, and an outer cladding region.

FIG. 5B depicts a relative refractive index profile of a glass fiberhaving a core region, an intermediate cladding region, and an outercladding region.

FIG. 6 depicts exemplary relative refractive index profiles of glassfibers.

FIG. 7 shows the dependence of puncture load on cross-sectional area forthree secondary coatings.

FIGS. 8A and 8B depict exemplary relative refractive index profiles ofglass fibers.

FIG. 9 shows an exemplary relative refractive index profile of a glassfiber.

FIG. 10 shows a plot of attenuation as a function of wavelength for twooptical fibers.

DETAILED DESCRIPTION

The present disclosure is provided as an enabling teaching and can beunderstood more readily by reference to the following description,drawings, examples, and claims. To this end, those skilled in therelevant art will recognize and appreciate that many changes can be madeto the various aspects of the embodiments described herein, while stillobtaining the beneficial results. It will also be apparent that some ofthe desired benefits of the present embodiments can be obtained byselecting some of the features without utilizing other features.Accordingly, those who work in the art will recognize that manymodifications and adaptations are possible and can even be desirable incertain circumstances and are a part of the present disclosure.Therefore, it is to be understood that this disclosure is not limited tothe specific compositions, articles, devices, and methods disclosedunless otherwise specified. It is also to be understood that theterminology used herein is for the purposes of describing particularaspects only and is not intended to be limiting.

In this specification and in the claims that follow, reference will bemade to a number of terms which shall be defined to have the followingmeanings:

“Include,” “includes,” or like terms means encompassing but not limitedto, that is, inclusive and not exclusive.

As used herein, the term “about” means that amounts, sizes,formulations, parameters, and other quantities and characteristics arenot and need not be exact, but may be approximate and/or larger orsmaller, as desired, reflecting tolerances, conversion factors, roundingoff, measurement error and the like, and other factors known to those ofskill in the art. When a value is said to be about or about equal to acertain number, the value is within ±10% of the number. For example, avalue that is about 10 refers to a value between 9 and 11, inclusive.When the term “about” is used in describing a value or an end-point of arange, the disclosure should be understood to include the specific valueor end-point referred to. Whether or not a numerical value or end-pointof a range in the specification recites “about,” the numerical value orend-point of a range is intended to include two embodiments: onemodified by “about,” and one not modified by “about.” It will be furtherunderstood that the end-points of each of the ranges are significantboth in relation to the other end-point, and independently of the otherend-point.

The term “about” further references all terms in the range unlessotherwise stated. For example, about 1, 2, or 3 is equivalent to about1, about 2, or about 3, and further comprises from about 1 to 3, fromabout 1 to 2, and from about 2 to 3. Specific and preferred valuesdisclosed for compositions, components, ingredients, additives, and likeaspects, and ranges thereof, are for illustration only; they do notexclude other defined values or other values within defined ranges. Thecompositions and methods of the disclosure include those having anyvalue or any combination of the values, specific values, more specificvalues, and preferred values described herein.

Where a range of numerical values is recited herein, comprising upperand lower values, unless otherwise stated in specific circumstances, therange is intended to include the endpoints thereof, and all integers andfractions within the range. It is not intended that the scope of theclaims be limited to the specific values recited when defining a range.Further, when an amount, concentration, or other value or parameter isgiven as a range, one or more preferred ranges or a list of upperpreferable values and lower preferable values, this is to be understoodas specifically disclosing all ranges formed from any pair of any upperrange limit or preferred value and any lower range limit or preferredvalue, regardless of whether such pairs are separately disclosed.

The indefinite article “a” or “an” and its corresponding definitearticle “the” as used herein means at least one, or one or more, unlessspecified otherwise.

As used herein, contact refers to direct contact or indirect contact.Direct contact refers to contact in the absence of an interveningmaterial and indirect contact refers to contact through one or moreintervening materials. Elements in direct contact touch each other.Elements in indirect contact do not touch each other, but do touch anintervening material or series of intervening materials, where theintervening material or at least one of the series of interveningmaterials touches the other. Elements in contact may be rigidly ornon-rigidly joined. Contacting refers to placing two elements in director indirect contact. Elements in direct (indirect) contact may be saidto directly (indirectly) contact each other.

As used herein, “directly adjacent” means directly contacting and“indirectly adjacent” mean indirectly contacting. The term “adjacent”encompasses elements that are directly or indirectly adjacent to eachother.

“Optical fiber” refers to a waveguide having a glass portion surroundedby a coating. The glass portion includes a core and a cladding. Thecladding surrounds and is directly adjacent to the core and includes twoor more concentric regions that differ in relative refractive index. Therelative refractive index of the core is greater than the relativerefractive index of the cladding. The glass portion of the optical fiberis referred to herein as a “glass fiber”.

“Radial position”, “radius”, or the radial coordinate “r” refers toradial position relative to the centerline (r=0) of the glass fiber.

The terms “inner” and “outer” are used to refer to relative values ofradial coordinate or relative positions of regions of the optical fiber,where “inner” means closer to the centerline of the fiber than “outer”.An inner radial coordinate is closer to the centerline of the glassfiber than an outer radial coordinate. An inner radial coordinate isbetween the centerline of the glass fiber and an outer radialcoordinate. An inner region of an optical fiber is closer to thecenterline of the glass fiber than an outer region. An inner region ofan optical fiber is between the centerline of the glass fiber and theouter region of the glass fiber.

The term “mode” refers to guided mode. A single-mode fiber is an opticalfiber designed to support only the fundamental LP01 modes over asubstantial length of the optical fiber (e.g., at least several meters),but that under certain circumstances can support multiple modes overshort distances (e.g., tens of centimeters). We assume that thebirefringence of the fiber is sufficiently low to assume that the twoorthogonally polarized components of the LP01 mode are degenerate andpropagate with the same phase velocity. A multimode optical fiber is anoptical fiber designed to support the fundamental LP01 modes and atleast one higher-order LP_(mm) mode over a substantial length of theoptical fiber, where either n≠0 or n≠1. The optical fibers disclosedherein are preferably single-mode optical fibers at a wavelength of 1550nm.

The “operating wavelength” of an optical fiber is the wavelength atwhich the optical fiber is operated. The operating wavelengthcorresponds to the wavelength of a guided mode. Representative operatingwavelengths include 850 nm, 980 nm, 1060 nm, 1310 nm and 1550 nm, whichare commonly used in telecommunications systems, optical data links, anddata centers. Although a particular operating wavelength may bespecified for an optical fiber, it is understood that a particularoptical fiber can operate at multiple operating wavelengths and/or overa continuous range of operating wavelengths. Characteristics such asmodal bandwidth and mode field diameter may vary with the operatingwavelength and the relative refractive index profile of a particularoptical fiber may be designed to provide optimal performance at aparticular operating wavelength, a particular combination of operatingwavelengths, or particular continuous range of operating wavelengths.

“Refractive index” refers to the refractive index at a wavelength of1550 nm.

The “refractive index profile” is the relationship between refractiveindex or relative refractive index and radius. For relative refractiveindex profiles depicted herein as having step boundaries betweenadjacent core and/or cladding regions, normal variations in processingconditions may preclude obtaining sharp step boundaries at the interfaceof adjacent regions. It is to be understood that although boundaries ofrefractive index profiles may be depicted herein as step changes inrefractive index, the boundaries in practice may be rounded or otherwisedeviate from perfect step function characteristics. It is furtherunderstood that the value of the relative refractive index may vary withradial position within the core region and/or any of the claddingregions. When relative refractive index varies with radial position in aparticular region of the fiber (e.g. core region and/or any of thecladding regions), it is expressed in terms of its actual or approximatefunctional dependence, or its value at a particular position within theregion, or in terms of an average value applicable to the region as awhole. Unless otherwise specified, if the relative refractive index of aregion (e.g. core region and/or any of the cladding regions) isexpressed as a single value or as a parameter (e.g. Δ or Δ %) applicableto the region as a whole, it is understood that the relative refractiveindex in the region is constant, or approximately constant, andcorresponds to the single value, or that the single value or parameterrepresents an average value of a non-constant relative refractive indexdependence with radial position in the region. For example, if “i” is aregion of the glass fiber, the parameter Δ_(i) refers to the averagevalue of relative refractive index in the region as defined by Eq. (2)below, unless otherwise specified. Whether by design or a consequence ofnormal manufacturing variability, the dependence of relative refractiveindex on radial position may be sloped, curved, or otherwisenon-constant.

“Relative refractive index,” as used herein, is defined in Eq. (1) as:

$\begin{matrix}{{{\Delta_{i}\left( r_{i} \right)}\%} = {100\frac{\left( {n_{i}^{2} - n_{ref}^{2}} \right)}{2n_{i}^{2}}}} & (1)\end{matrix}$

where n_(i) is the refractive index at radial position r_(i) in theglass fiber, unless otherwise specified, and n_(ref) is the refractiveindex of pure silica glass, unless otherwise specified. Accordingly, asused herein, the relative refractive index percent is relative to puresilica glass, which has a refractive index of 1.444 at a wavelength of1550 nm. As used herein, the relative refractive index is represented byΔ (or “delta”) or Δ % (or “delta %) and its values are given in units of“%”, unless otherwise specified. Relative refractive index may also beexpressed as Δ(r) or Δ(r) %.

The average relative refractive index (Δ_(ave)) of a region of the fiberis determined from Eq. (2):

$\begin{matrix}{\Delta_{ave} = {\int_{r_{inner}}^{r_{outer}}\frac{{\Delta (r)}{dr}}{\left( {r_{outer} - r_{inner}} \right)}}} & (2)\end{matrix}$

where r_(inner) is the inner radius of the region, r_(outer) is theouter radius of the region, and Δ(r) is the relative refractive index ofthe region.

The term “α-profile” refers to a relative refractive index profile Δ(r)that has the functional form defined in Eq. (3):

$\begin{matrix}{{\Delta (r)} = {{\Delta \left( r_{0} \right)}\left\lbrack {1 - \left\lbrack \frac{{r - r_{0}}}{\left( {r_{z} - z_{0}} \right)} \right\rbrack^{\alpha}} \right\rbrack}} & (3)\end{matrix}$

where r_(o) is the radial position at which Δ(r) is maximum, r_(z)>r₀ isthe radial position at which Δ(r) decreases to its minimum value, and ris in the range r_(i)≤r≤r_(f), where r_(i) is the initial radialposition of the α-profile, r_(f) is the final radial position of theα-profile, and α is a real number. Δ(r₀) for an α-profile may bereferred to herein as Δ_(max) or, when referring to a specific region iof the fiber, as Δ_(i,max). When the relative refractive index profileof the fiber core region is described by an α-profile with r₀ occurringat the centerline (r=0) and r_(z) corresponding to the outer radius r₁of the core region, and Δ₁(r₁)=0, Eq. (3) simplifies to Eq. (4):

$\begin{matrix}{{\Delta_{1}(r)} = {\Delta_{1\max}\left\lbrack {1 - \left\lbrack \frac{r}{r_{1}} \right\rbrack^{\alpha}} \right\rbrack}} & (4)\end{matrix}$

The term “super-Gaussian profile” refers to a relative refractive indexprofile Δ(r) that has the functional form defined in Eq. (5):

$\begin{matrix}{{\Delta_{1}(r)} = {\Delta_{1\max}{\exp \left( {- \left( \frac{r}{a} \right)^{\gamma}} \right)}}} & (5)\end{matrix}$

where r is the radial distance from the centerline, γ is a positivenumber, and a is a radial scaling parameter such that when r=a,Δ₁=Δ_(1max)/e.

The “mode field diameter” or “MFD” of an optical fiber is defined in Eq.(6) as:

$\begin{matrix}{{{MFD} = {2w}}{w^{2} = {2\frac{\int_{0}^{\infty}{\left( {f(r)} \right)^{2}{rdr}}}{\int_{0}^{\infty}{\left( \frac{\left( {{df}(r)} \right.}{dr} \right)^{2}{rdr}}}}}} & (6)\end{matrix}$

where f(r) is the transverse component of the electric fielddistribution of the guided optical signal and r is radial position inthe fiber. “Mode field diameter” or “MFD” depends on the wavelength ofthe optical signal and is reported herein for a wavelength of 1550 nm.Specific indication of the wavelength will be made when referring tomode field diameter herein. Unless otherwise specified, mode fielddiameter refers to the LP₀₁ mode at the specified wavelength.

“Effective area” of an optical fiber is defined in Eq. (7) as:

$\begin{matrix}{A_{eff} = \frac{2{\pi \left\lbrack {\int_{0}^{\infty}{\left( {f(r)} \right)^{2}{rdr}}} \right\rbrack}^{2}}{\int_{0}^{\infty}{\left( {f(r)} \right)^{4}{rdr}}}} & (7)\end{matrix}$

where f(r) is the transverse component of the electric field of theguided optical signal and r is radial position in the fiber. “Effectivearea” or “A_(eff)” depends on the wavelength of the optical signal andis understood herein to refer to a wavelength of 1550 nm.

“Trench region” refers to a region of the cladding of a glass fiber thatis surrounded by and directly adjacent to an outer cladding region. Thetrench region extends from an inner radial coordinate r_(Trench, inner)to an outer radial coordinate r_(Trench,outer). The relative refractiveindex at all radial positions in the trench region is less than therelative refractive index of the outer cladding region.

“Trench volume” of a trench region is defined as:

$\begin{matrix}{V_{Trench} = {{2{\int_{r_{{Trench},{inner}}}^{r_{{Trench},{outer}}}{\left( {{\Delta_{Trench}(r)} - \Delta_{4}} \right){rdr}}}}}} & (8)\end{matrix}$

where r_(Treneh,inner) is the inner radius of the trench region,r_(Trench,outer) is the outer radius of the trench region, Δ₄ is therelative refractive index of the outer cladding region that surroundsand is directly adjacent to the trench region, and Δ_(Trench)(r) is therelative refractive index of the trench, where Δ_(Trench)(r)<Δ₄ at allradial positions between r_(Trench,inner) and r_(Trench,outer). Thetrench region is also referred to herein as an intermediate claddingregion. In the present disclosure, r_(Trench,inner) is referred to as r₁(in embodiments without an inner cladding region) or r₂ (in embodimentswith an inner cladding region), r_(Trench,outer) is referred to as r₃,and Δ_(Trench) is referred to as Δ₃. V_(Trench) may also be referred toas V₃. Trench volume is defined as an absolute value and has a positivevalue. Trench volume is expressed herein in units of % Δmicron², %Δ-micron², % Δ-μm², or % Δμm², whereby these units can be usedinterchangeably herein.

The “cutoff wavelength” of an optical fiber is the minimum wavelength atwhich the optical fiber will support only one propagating mode. Forwavelengths below the cutoff wavelength, multimode transmission mayoccur and multipath interference between the LP₀₁ and one or more higherorder modes may arise to limit the information carrying capacity of theoptical fiber. Cutoff wavelength will be reported herein as a fibercutoff wavelength or a cable cutoff wavelength. The fiber cutoffwavelength is based on a 2-meter fiber length and the cable cutoffwavelength is based on a 22-meter cabled fiber length. The 22-metercable cutoff wavelength is typically less than the 2-meter cutoffwavelength due to higher levels of bending and mechanical pressure inthe cable environment. The fiber cutoff wavelength λ_(CF) is based on a2-meter fiber length while the cable cutoff wavelength λ_(CC) is basedon a 22-meter cabled fiber length as specified in TIA-455-80: FOTP-80IEC-60793-1-44 Optical Fibres—Part 1-44: Measurement Methods and TestProcedures—Cut-off Wavelength (21 May 2003), by TelecommunicationsIndustry Association (TIA).

“Chromatic dispersion”, herein referred to as “dispersion” unlessotherwise noted, of an optical fiber is the sum of the materialdispersion, the waveguide dispersion, and the intermodal dispersion. Inthe case of single mode waveguide fibers, the intermodal dispersion iszero. Dispersion values in a two-mode regime assume intermodaldispersion is zero. The zero-dispersion wavelength (λ₀) is thewavelength at which the dispersion has a value of zero.

The “spring constant” χ_(p) of a primary coating is computed from Eq.(9):

$\begin{matrix}{\chi_{p} = \frac{E_{p}d_{}}{t_{p}}} & (9)\end{matrix}$

where E_(p) is the in situ modulus of the primary coating, t_(p) is thethickness of the primary coating, and d_(g) is the diameter 2r₄ of theglass fiber. The spring constant is a phenomenological parameter thatdescribes the extent to which the primary coating mitigates coupling ofthe secondary coating to the glass fiber. (See “Relationship ofMechanical Characteristics of Dual Coated Single Mode Optical Fibers andMicrobending Loss”, by J. Baldauf et al., IEICE Transactions onCommunications, Vol. E76-B, No. 4, pp. 352-357 (1993)) In thephenomenological model, the buffering effect of the primary coating ismodeled as a spring with the spring constant given in Eq. (9). A lowspring constant leads to greater resistance to microbending. Thetradeoff of in situ modulus and thickness in establishing the resistanceof the primary coating to microbending is reflected in the springconstant.

The optical fibers disclosed herein include a core region, a claddingregion surrounding the core region, and a coating surrounding thecladding region. The core region and cladding region are glass anddefine a glass fiber. The cladding region includes multiple regions, atleast two of which differ in relative refractive index. In oneembodiment, the multiple cladding regions are concentric regions thatinclude an intermediate cladding region surrounding and directlyadjacent to the core region and an outer cladding region surrounding anddirectly adjacent to the intermediate cladding region. In anotherembodiment, the multiple cladding regions are concentric regions thatinclude an inner cladding region surrounding and directly adjacent tothe core region, an intermediate cladding region surrounding anddirectly adjacent to the inner cladding region, and an outer claddingregion surrounding and directly adjacent to the intermediate claddingregion. The intermediate cladding region has a lower relative refractiveindex than the outer cladding region. The intermediate cladding regionmay also be referred to herein as a trench or trench region and has atrench volume given by Eq. (8). The intermediate cladding region maycontribute to a reduction in bending losses. The core region, claddingregion, inner cladding region, intermediate cladding region, and outercladding region are also referred to as core, cladding, inner cladding,intermediate cladding, and outer cladding, respectively. All embodimentsof the optical fiber include a glass fiber with a core, an intermediatecladding, and an outer cladding. In some embodiments, the glass fiberalso includes an inner cladding between the intermediate cladding andcore; that is, the inner cladding is optional.

Whenever used herein, radial position r₁ and relative refractive indexΔ₁ or Δ₁(r) refer to the core region, radial position r₂ and relativerefractive index Δ₂ or Δ₂(r) refer to the inner cladding region, radialposition r₃ and relative refractive index Δ₃ or Δ₃(r) refer to theintermediate cladding region, radial position r₄ and relative refractiveindex Δ₄ or Δ₄(r) refer to the outer cladding region, radial position r₅refers to the primary coating, radial position r₆ refers to thesecondary coating, and radial position r₇ refers to the tertiarycoating.

The relative refractive index Δ₁(r) has a maximum value Δ_(1max) and aminimum value Δ_(1min). The relative refractive index Δ₂(r) has amaximum value Δ_(2max) and a minimum value Δ_(2min). The relativerefractive index Δ₃(r) has a maximum value Δ_(3max) and a minimum valueΔ_(3min). The relative refractive index Δ₄(r) has a maximum valueΔ_(4max) and a minimum value Δ_(4min). In embodiments in which therelative refractive index is constant or approximately constant over aregion, the maximum and minimum values of the relative refractive indexare equal or approximately equal. Unless otherwise specified, if asingle value is reported for the relative refractive index of a region,the single value corresponds to an average value for the region.

It is understood that the central core region is substantiallycylindrical in shape and that a surrounding inner cladding region, asurrounding intermediate cladding region, a surrounding outer claddingregion, a surrounding primary coating, a surrounding secondary coating,and a surrounding tertiary coating are substantially annular in shape.Annular regions may be characterized in terms of an inner radius and anouter radius. Radial positions r₁, r₂, r₃, r₄, r₅, r₆, and r₇ referherein to the outer radii of the core, inner cladding, intermediatecladding, outer cladding, primary coating, secondary coating, andtertiary coating, respectively. The radius r₄ defines the outer boundaryof the glass fiber. The radius r₆ also corresponds to the outer radiusof the optical fiber in embodiments without a tertiary coating. When atertiary coating is present, the radius r₇ corresponds to the outerradius of the optical fiber.

When two regions are directly adjacent to each other, the outer radiusof the inner of the two regions coincides with the inner radius of theouter of the two regions. For example, the glass fibers disclosed hereininclude an intermediate cladding region surrounded by and directlyadjacent to an outer cladding region. In such an embodiment, the radiusr₃ corresponds to the outer radius of the intermediate cladding regionand the inner radius of the outer cladding region.

As noted above, the inner cladding region is optional. In embodimentswith an inner cladding region, the radius r₂ corresponds to the outerradius of the inner cladding region and the inner radius of theintermediate cladding region. In embodiments without an inner claddingregion, the radius r₁ corresponds to the outer radius of the core regionand the inner radius of the intermediate cladding region. That is, inembodiments without an inner cladding region, the intermediate claddingregion is directly adjacent to the core region.

The following terminology applies to embodiments in which the relativerefractive index profile includes an inner cladding region surroundingand directly adjacent to the core, an intermediate cladding regionsurrounding and directly adjacent to the inner cladding region, an outercladding region surrounding and directly adjacent to the intermediatecladding region, a primary coating surrounding and directly adjacent tothe outer cladding region, and a secondary coating surrounding anddirectly adjacent to the primary coating. The difference between radialposition r₂ and radial position r₁ is referred to herein as thethickness of the inner cladding region. The difference between radialposition r₃ and radial position r₂ is referred to herein as thethickness of the intermediate cladding region. The difference betweenradial position r₄ and radial position r₃ is referred to herein as thethickness of the outer cladding region. The difference between radialposition r₅ and radial position r₄ is referred to herein as thethickness of the primary coating. The difference between radial positionr₆ and radial position r₅ is referred to herein as the thickness of thesecondary coating. The difference between radial position r₇ and radialposition r₆ is referred to herein as the thickness of the tertiarycoating.

The following terminology applies to embodiments in which anintermediate cladding region is directly adjacent to a core region andan outer cladding region is directly adjacent the intermediate claddingregion. The difference between radial position r₃ and radial position r₁is referred to herein as the thickness of the intermediate claddingregion. The difference between radial position r₄ and radial position r₃is referred to herein as the thickness of the outer cladding region. Thedifference between radial position r₅ and radial position r₄ is referredto herein as the thickness of the primary coating. The differencebetween radial position r₆ and radial position r₅ is referred to hereinas the thickness of the secondary coating. The difference between radialposition r₇ and radial position r₆ is referred to herein as thethickness of the tertiary coating.

As will be described further hereinbelow, the relative refractiveindices of the core region, intermediate cladding region, and outercladding region differ. The relative refractive index Δ₂ of the innercladding region is less than the relative refractive index Δ₁ of thecore region and greater than the relative refractive index Δ₃ of theintermediate cladding region. The relative refractive index Δ₂ of theinner cladding region may be less than, equal to, or greater than therelative refractive index Δ₄ of the outer cladding region. Each of theregions is formed from doped or undoped silica glass. Variations inrefractive index relative to undoped silica glass are accomplished byincorporating updopants or downdopants at levels designed to provide atargeted refractive index or refractive index profile using techniquesknown to those of skill in the art. Updopants are dopants that increasethe refractive index of the glass relative to the undoped glasscomposition. Downdopants are dopants that decrease the refractive indexof the glass relative to the undoped glass composition. In oneembodiment, the undoped glass is pure silica glass. When the undopedglass is pure silica glass, updopants include Cl, Br, Ge, Al, P, Ti, Zr,Nb, and Ta, and downdopants include F and B. Regions of constantrefractive index may be formed by not doping or by doping at a uniformconcentration. Regions of variable refractive index are formed throughnon-uniform spatial distributions of dopants and/or throughincorporation of different dopants in different regions. Refractiveindex varies approximately linearly with the concentration of theupdopant or downdopant. For example, each 1 wt % Cl as a dopant insilica glass increases the relative refractive index by about 0.083 Δ %and each 1 wt % F as a dopant in silica glass decreases the relativerefractive index by about 0.32 Δ %.

The coatings described herein are formed from curable coatingcompositions. Curable coating compositions include one or more curablecomponents. As used herein, the term “curable” is intended to mean thatthe component, when exposed to a suitable source of curing energy,includes one or more curable functional groups capable of formingcovalent bonds that participate in linking the component to itself or toother components of the coating composition. The product obtained bycuring a curable coating composition is referred to herein as the curedproduct of the composition. The cured product is preferably a polymer.The curing process is induced by energy. Forms of energy includeradiation or thermal energy. In a preferred embodiment, curing occurswith radiation, where radiation refers to electromagnetic radiation.Curing induced by radiation is referred to herein as radiation curing orphotocuring. A radiation-curable component is a component that can beinduced to undergo a curing reaction when exposed to radiation of asuitable wavelength at a suitable intensity for a sufficient period oftime. Suitable wavelengths include wavelengths in the infrared, visible,or ultraviolet portion of the electromagnetic spectrum. The radiationcuring reaction occurs in the presence of a photoinitiator. Aradiation-curable component may also be thermally curable. Similarly, athermally curable component is a component that can be induced toundergo a curing reaction when exposed to thermal energy of sufficientintensity for a sufficient period of time. A thermally curable componentmay also be radiation curable.

A curable component includes one or more curable functional groups. Acurable component with only one curable functional group is referred toherein as a monofunctional curable component. A curable component havingtwo or more curable functional groups is referred to herein as amultifunctional curable component. Multifunctional curable componentsinclude two or more functional groups capable of forming covalent bondsduring the curing process and can introduce crosslinks into thepolymeric network formed during the curing process. Multifunctionalcurable components may also be referred to herein as “crosslinkers” or“curable crosslinkers”. Curable components include curable monomers andcurable oligomers. Examples of functional groups that participate incovalent bond formation during the curing process are identifiedhereinafter.

The term “molecular weight” when applied to polyols means number averagemolecular weight (M_(n)).

The term “(meth)acrylate” means methacrylate, acrylate, or a combinationof methacrylate and acrylate.

Values of in situ modulus, Young's modulus, % elongation, and tearstrength refer to values as determined under the measurement conditionsby the procedures described herein.

Reference will now be made in detail to illustrative embodiments of thepresent description.

The optical fibers disclosed herein include a glass fiber surrounded bya coating. An example of an optical fiber is shown in schematiccross-sectional view in FIG. 1. Optical fiber 10 includes a glass fiber11 surrounded by primary coating 16 and secondary coating 18. Furtherdescription of glass fiber 11, primary coating 16, and secondary coating18 is provided below.

FIG. 2 illustrates an optical fiber ribbon 30. The ribbon 30 includes aplurality of optical fibers 20 and a matrix 32 encapsulating theplurality of optical fibers. Optical fibers 20 include a core region, acladding region, a primary coating, and a secondary coating as describedabove. Optical fibers 20 may also include a tertiary coating as notedabove. The secondary coating may include a pigment. The optical fibers20 are aligned relative to one another in a substantially planar andparallel relationship. The optical fibers in fiber optic ribbons areencapsulated by the ribbon matrix 32 in any known configuration (e.g.,edge-bonded ribbon, thin-encapsulated ribbon, thick-encapsulated ribbon,or multi-layer ribbon) by conventional methods of making fiber opticribbons. In FIG. 2, the fiber optic ribbon 30 contains twelve (12)optical fibers 20; however, it should be apparent to those skilled inthe art that any number of optical fibers 20 (e.g., two or more) may beemployed to form fiber optic ribbon 30 disposed for a particular use.The ribbon matrix 32 can be formed from the same composition used toprepare a secondary coating, or the ribbon matrix 32 can be formed froma different composition that is otherwise compatible for use.

FIG. 3 illustrates an optical fiber cable 40. Cable 40 includes aplurality of optical fibers 20 surrounded by jacket 42. Optical fibers20 may be densely or loosely packed into a conduit enclosed by innersurface 44 of jacket 42. The number of fibers placed in jacket 42 isreferred to as the “fiber count” of optical fiber cable 40. The jacket42 is formed from an extruded polymer material and may include multipleconcentric layers of polymers or other materials. Optical fiber cable 40may include one or more strengthening members (not shown) embeddedwithin jacket 42 or placed within the conduit defined by inner surface44. Strengthening members include fibers or rods that are more rigidthan jacket 42. The strengthening member is made from metal, braidedsteel, glass-reinforced plastic, fiberglass, or other suitable material.Optical fiber cable 40 may include other layers surrounded by jacket 42(e.g. armor layers, moisture barrier layers, rip cords, etc.). Opticalfiber cable 40 may have a stranded, loose tube core or other fiber opticcable construction.

Glass Fiber. The optical fibers disclosed herein include a glass fiberwith a core region, a cladding region surrounding the core region, and acoating surrounding the cladding region. The core region and claddingregion are glass. Glass fiber 11 includes a core region 12 and acladding region 14, as is familiar to the skilled artisan. Core region12 has a higher refractive index than cladding region 14 and glass fiber11 functions as a waveguide.

In many applications, the core region and cladding region have adiscernible core-cladding boundary. Alternatively, the core region andcladding region can lack a distinct boundary. One type of fiber is astep-index fiber. Another type of fiber is a graded-index fiber, whichhas a core region with a refractive index that varies with distance fromthe fiber center. Examples of graded-index fibers are fibers with a coreregion having a relative refractive index profile with an α-profiledefined by Eq. (4) above or the super-Gaussian profile defined by Eq.(5) above.

A schematic cross-sectional depiction of an optical fiber is shown inFIGS. 4A and 4B. In FIG. 4A, optical fiber 46 includes core region 48,cladding region 50, primary coating 56, and secondary coating 58.Cladding region 50 includes inner cladding region 51, intermediatecladding region 53 and outer cladding region 55. In FIG. 4B, opticalfiber 46 includes core region 48, cladding region 50, primary coating56, and secondary coating 58. Cladding region 50 includes intermediatecladding region 53 and outer cladding region 55.

A representative relative refractive index profile for a glass fiber ispresented in FIGS. 5A and 5B. FIG. 5A shows a rectangular trench profilefor a glass fiber 60 having a core region (1) with outer radius r₁ andrelative refractive index Δ₁ with maximum relative refractive indexΔ_(1max), an inner cladding region (2) extending from radial position r₁to radial position r₂ and having relative refractive index Δ₂, anintermediate cladding region (3) extending from radial position r₂ toradial position r₃ and having relative refractive index Δ₃, and an outercladding region (4) extending from radial position r₃ to radial positionr₄ and having relative refractive index Δ₄.

FIG. 5B shows a rectangular trench profile for a glass fiber 60 having acore region (1) with outer radius r₁ and relative refractive index Δ₁with maximum relative refractive index Δ_(1max), an intermediatecladding region (3) extending from radial position r₁ to radial positionr₃ and having relative refractive index Δ₃, and an outer cladding region(4) extending from radial position r₃ to radial position r₄ and havingrelative refractive index Δ₄.

In the profiles of FIGS. 5A and 5B, the intermediate cladding region (3)is a trench with a constant or average relative refractive index Δ₃ thatis less than the constant or average relative refractive index Δ₄ of theouter cladding region (4). The intermediate cladding region (3) has atrench volume as defined in Eq. (8) above. Core region (1) has thehighest average and maximum relative refractive index in the profile.Core region (1) may include a lower index region at or near thecenterline (known in the art as a “centerline dip”) (not shown).

In the profiles shown in FIGS. 5A and 5B, the core region (1) of theglass fiber has a graded index with a relative refractive indexdescribed by a super-Gaussian profile. The radial position r₀(corresponding to Δ_(1max)) of the super-Gaussian profile corresponds tothe centerline (r=0) of the fiber and the radial position r_(z) of thesuper-Gaussian profile corresponds to the core radius r₁. In embodimentswith a centerline dip, the radial position r₀ is slightly offset fromthe centerline of the fiber. In other embodiments (not shown), coreregion (1) is a step index relative refractive index profile or anα-profile relative refractive index profile instead of a super-Gaussianprofile. In still other embodiments, core region (1) has a relativerefractive index profile not defined by any of an α-profile, asuper-Gaussian profile, or a step-index profile. In some embodiments,the relative refractive index Δ₁ continuously decreases in the radialdirection away from the centerline. In other embodiments, relativerefractive index Δ₁ varies over some radial positions between thecenterline and r₁, and also includes a constant or approximatelyconstant value over other radial positions between the centerline andr₁.

In the profile shown in FIG. 5A, transition region 62 from innercladding region (2) to intermediate cladding region (3) and transitionregion 64 from intermediate cladding region (3) to outer cladding region(4) are shown as step changes. It is to be understood that a step changeis an idealization and that transition region 62 and transition region64 may not be strictly vertical in practice. Instead, transition region62 and/or transition region 64 may have a slope or curvature. Whentransition region 62 and/or transition region 64 are non-vertical, theinner radius r₂ and outer radius r₃ of intermediate cladding region (3)correspond to the mid-points of transition regions 62 and 64,respectively. The mid-points correspond to half of the depth 67 of theintermediate cladding region (3) relative to the outer cladding region(4).

The relative ordering of relative refractive indices Δ₁, Δ₂, Δ₃, and Δ₄in the relative refractive index profile shown in FIG. 5A satisfy theconditions Δ_(1max)>Δ₄>Δ₃ and Δ_(1max)>Δ₂>Δ₃.

In the profile shown in FIG. 5B, transition region 62 from core region(1) to intermediate cladding region (3) and transition region 64 fromintermediate cladding region (3) to outer cladding region (4) are shownas step changes. It is to be understood that a step change is anidealization and that transition region 62 and transition region 64 maynot be strictly vertical in practice. Instead, transition region 62and/or transition region 64 may have a slope or curvature. Whentransition region 62 and/or transition region 64 are non-vertical, theinner radius r₁ and outer radius r₃ of intermediate cladding region (3)correspond to the mid-points of transition regions 62 and 64,respectively. The mid-points correspond to half of the depth 67 of theintermediate cladding region (3) relative to the outer cladding region(4).

The relative ordering of relative refractive indices Δ₁, Δ₃, and Δ₄ inthe relative refractive index profile shown in FIG. 5B satisfy thecondition Δ_(1max)>Δ₄>Δ₃.

The core region comprises silica glass. Preferably, the silica glass ofthe core region is Ge-free; that is the core region comprises silicaglass that lacks Ge. The silica glass of the core region is undopedsilica glass, updoped silica glass, and/or downdoped silica glass.Updoped silica glass includes silica glass doped with an alkali metaloxide (e.g. Na₂O, K₂O, Li₂O, Cs₂O, or Rb₂O). Downdoped silica glassincludes silica glass doped with F. In some embodiments, the core regionis co-doped with alkali metal oxide and fluorine. The concentration ofalkali metal oxide (e.g. K₂O) in the core, expressed in terms of theamount of alkali metal (e.g. K), is in the range from 20 ppm to 500 ppm,or 35 ppm to 400 ppm, or 50 ppm to 300 ppm, where ppm refers to partsper million by weight.

In some embodiments, the core region includes an updopant and adowndopant, where the concentration of updopant is highest at thecenterline (r=0) and lowest at the radius r₁ and the concentration ofdowndopant is lowest at the centerline (r=0) and highest at the radiusr₁. In such embodiments, the relative refractive index Δ₁ may have apositive value near the centerline (r=0) and decrease to a negativevalue at the radius r₁.

In one embodiment, the core region is a segmented core region thatincludes an inner core region surrounded by an outer core region, wherethe inner core region comprises updoped silica glass and has a positivemaximum relative refractive index Δ_(1max), and the outer core regioncomprises downdoped silica glass and has a negative minimum relativerefractive index Δ_(1min). The updoped silica glass of the inner coreregion includes an updopant or a combination of an updopant anddowndopant. In embodiments in which the inner core region includes acombination of an updopant and downdopant, the relative concentrationsof updopant and downdopant are adjusted to provide a net positive valueof the maximum relative refractive index. In embodiments in which theouter core region includes a combination an updopant and downdopant, therelative concentrations of updopant and downdopant are adjusted toprovide a net negative value of the relative refractive index. Inembodiments with a segmented core, Δ₁ (and Δ_(1max) and Δ_(1min)) referto the entirety of the core region, including the inner core region andthe outer core region, r₁ corresponds to the outer radius of the outercore region, and r_(a) corresponds to the outer radius of the inner coreregion. The boundary between the inner core region and outer core regionoccurs at radial position r_(a), where r_(a)<r₁.

In some embodiments, the relative refractive index of the core region ofthe glass fiber is described by an α-profile with an α value in therange from 1.5 to 10, or in the range from 1.7 to 8.0, or in the rangefrom 1.8 to 6.0, or in the range from 1.9 to 5.0, or in the range from1.95 to 4.5, or in the range from 2.0 to 4.0, or in the range from 4.0to 9.5, or in the range from 5.0 to 9.0, or in the range from 10 to 100,or in the range from 11 to 40, or in the range from 12 to 30. As thevalue of a increases, the relative refractive profile more closelyapproaches a step index profile. In some embodiments with a segmentedcore region, either or both of the inner core region and outer coreregion has a relative refractive index described by an α-profile with ana value as described herein.

The outer radius r₁ of the core region is in the range from 3.0 μm to10.0 μm, or in the range from 3.5 μm to 9.0 μm, or in the range from 4.0μm to 8.0 μm. In some embodiments, the core region includes a portionwith a constant or approximately constant relative refractive index thathas a width in the radial direction of at least 1.0 μm, or at least 2.0μm, or at least 3.0 μm, or at least 4.0 μm, or at least 5.0 μm, or inthe range from 1.0 μm to 6.0 μm, or in the range from 2.0 μm to 5.0 μm.In an embodiment, the portion of the core region having a constant orapproximately constant relative refractive index has a relativerefractive index of Δ_(1min). In embodiments with a segmented coreregion, the radius r_(a) is in the range from 0.25 μm to 3.0 μm, or inthe range from 0.5 μm to 2.5 μm, or in the range from 0.75 μm to 2.0 μm.

The relative refractive index Δ₁ or Δ_(1max) of the core region is inthe range from −0.15% to 0.30%, or in the range from −0.10% to 0.20%, orin the range from −0.05% to 0.15%, or in the range from 0.00% to 0.10%.The minimum relative refractive index Δ_(1min) of the core is in therange from −0.20% to 0.10%, or in the range from −0.15% to 0.05%, or inthe range from −0.15% to 0.00%.

In some embodiments, the relative refractive index of the core region isdescribed by a step-index profile having a constant or approximatelyconstant value corresponding to Δ_(1max).

The inner cladding region comprises undoped silica glass, updoped silicaglass, or downdoped silica glass. The relative refractive index Δ₂ ofthe inner cladding region is in the range from −0.60% to 0.00%, or inthe range from −0.55% to −0.05%, or in the range from −0.50% to −0.10%,or in the range from −0.45% to −0.15%. The relative refractive index Δ₂is preferably constant or approximately constant. The difference Δ₂ toΔ₃ (or the difference Δ₂ to Δ_(3min), or the difference Δ_(2max) to Δ₃,or the difference Δ_(2max) to Δ_(3min)) is greater than 0.10%, orgreater than 0.15%, or greater than 0.20%, or greater than 0.25%, orgreater than 0.30%, or in the range from 0.10% to 0.40%, or in the rangefrom 0.15% to 0.35%. The relative refractive index Δ₂ of the innercladding region is less than, equal to, or greater than the relativerefractive index Δ₄ of the outer cladding region.

The inner radius of the inner cladding region is r₁ and has the valuesgiven above. The outer radius r₂ of the inner cladding region is in therange from 6.0 μm to 18.0 μm, or in the range from 7.0 μm to 16.0 μm, orin the range from 8.0 μm to 14.0 μm. The thickness r₂−r₁ of the innercladding region is in the range from 2.0 μm to 10.0 μm, or in the rangefrom 3.0 μm to 9.0 μm, or in the range from 4.0 μm to 8.0 μm.

The intermediate cladding region comprises downdoped silica glass. Thepreferred downdopant is F (fluorine). The concentration of F (fluorine)is in the range from 0.1 wt % to 2.5 wt %, or in the range from 0.25 wt% to 2.25 wt %, or in the range from 0.3 wt % to 2.0 wt %.

In embodiments in which the relative refractive index profile includesan intermediate cladding region, the relative refractive index Δ₃ orΔ_(3min) is in the range from −0.30% to −0.90%, or in the range from−0.30% to −0.70%, or in the range from −0.30% to −0.60%, or in the rangefrom −0.30% to −0.50%, or in the range from −0.35% to −0.75%, or in therange from −0.35% to −0.60%, or in the range from −0.40% to −0.70%, orin the range from −0.45% to −0.70%. The relative refractive index Δ₃ ispreferably constant or approximately constant. The difference Δ_(1max)to r₃ (or the difference Δ_(1max) to Δ_(3min), or the difference Δ₁ toΔ₃, or the difference Δ₁ to Δ_(3min)) is greater than 0.20%, or greaterthan 0.30%, or greater than 0.40%, or greater than 0.50%, or greaterthan 0.60%, or in the range from 0.25% to 0.70%, or in the range from0.35% to 0.60%. The difference Δ_(1min) to Δ₃ (or the differenceΔ_(1min) to Δ_(3min)) is greater than 0.20%, or greater than 0.30%, orgreater than 0.40%, or greater than 0.50%, or in the range from 0.20% to0.60%, or in the range from 0.25% to 0.50%.

The inner radius of the intermediate cladding region is r₁ (inembodiments without an inner cladding region) or r₂ (in embodiments withan inner cladding region) and has the values specified above. The outerradius r₃ of the intermediate cladding region is in the range from 10.0μm to 30.0 μm, or in the range from 12.5 μm to 27.5 μm, or in the rangefrom 15.0 μm to 25.0 μm. The thickness r₃−r₁ (in embodiments without aninner cladding region) or the thickness r₃−r₂ (in embodiments with aninner cladding region) of the intermediate cladding region is in therange from 2.0 μm to 22.0 μm, or in the range from 5.0 μm to 20.0 μm, orin the range from or in the range from 7.5 μm to 17.5 μm, or in therange from 10.0 μm to 15.0 μm.

In embodiments having an inner cladding region, the trench volumeV_(Trench) of the intermediate cladding region is greater than 20% μm²,or greater than 30% Δμm², or greater than 40% Δμm², or greater than 50%Δμm², or greater than 60% Δμm², or in the range from 20% Δμm² to 70%Δμm², or in the range from 25% Δμm² to 65% Δμm², or in the range from30% Δμm² to 60% Δμm². Trench volume can be controlled by varying thethickness of the intermediate cladding region, the relative refractiveindex of the intermediate cladding region and/or the difference betweenthe relative refractive index of the outer cladding region and therelative refractive index of the intermediate cladding region.

In embodiments without an inner cladding region, the trench volumeV_(Trench) of the intermediate cladding region is greater than 10.0%Δμm², or greater than 15.0% Δμm², or greater than 20.0% Δμm², or greaterthan 25.0% Δμm², or greater than 30.0% Δμm², or in the range from 10.0%Δμm² to 40.0% Δμm², or in the range from 15.0% Δμm² to 35.0% Δμm², or inthe range from 20.0% Δμm² to 30.0% Δμm². Trench volume can be controlledby varying the thickness of the intermediate cladding region, therelative refractive index of the intermediate cladding region and/or thedifference between the relative refractive index of the outer claddingregion and the relative refractive index of the intermediate claddingregion.

The relative refractive index Δ₄ or Δ_(4max) of the outer claddingregion is in the range from −0.60% to 0.00%, or in the range from −0.55%to −0.05%, or in the range from −0.50% to −0.10%, or in the range from−0.45% to −0.15%, or in the range from −0.40% to −0.20%, or in the rangefrom −0.35% to −0.25%. The relative refractive index Δ₄ is preferablyconstant or approximately constant. The difference Δ₄ to Δ₃ (or thedifference Δ₄ to Δ_(3min), or the difference Δ_(4max) to Δ₃, or thedifference Δ_(4max) to Δ_(3min)) is greater than 0.10%, or greater than0.20%, or greater than 0.25%, or greater than 0.30%, or greater than0.35%, or in the range from 0.10% to 0.45%, or in the range from 0.15%to 0.40%.

The inner radius of the outer cladding region is r₃ and has the valuesspecified above. The outer radius r₄ is preferably low to minimize thediameter of the glass fiber to facilitate high fiber count in a cable.The outer radius r₄ of the outer cladding region is less than or equalto 52.5 μm, or less than or equal to 50.0 μm, or less than or equal to47.5 μm, or less than or equal to 45.0 μm, or less than or equal to 42.5μm, or less than or equal to 40.0 μm, or in the range from 37.5 μm to52.5 μm, or in the range from 37.5 μm to 50.0 μm, or in the range from37.5 μm to 47.5 μm, or in the range from 40.0 μm to 52.5 μm, or in therange from 40.0 μm to 50.0 μm, or in the range from 40.0 μm to 47.5 μm,or in the range from 42.5 μm to 50.0 μm. The thickness r₄−r₃ of theouter cladding region is in the range from 15.0 μm to 40.0 μm, or in therange from 17.5 μm to 37.5 μm, or in the range from 20.0 μm to 35.0 μm,or in the range from 22.5 μm to 32.5 μm.

FIG. 6 illustrates representative relative refractive index profiles ofmanufactured glass fibers. Relative refractive index profiles 70 and 80include, in the direction of increasing radial position, a core region,an intermediate cladding region, and an outer cladding region. Relativerefractive index profiles 90 and 100 include, in the direction ofincreasing radial position, a core region, an inner cladding region, anintermediate cladding region, and an outer cladding region. The widthand depth of the intermediate cladding region varies. Relativerefractive index profile 70 includes transition region 73 between a coreregion and a depressed index cladding region and transition region 77between a depressed index region and an outer cladding region.Transition region 73 occurs at radius r₁ and transition region 77 occursat radius r₃ for relative refractive index profile 70. Relativerefractive index profile 80 includes transition region 83 between a coreregion and a depressed index cladding region and transition region 87between a depressed index region and an outer cladding region.Transition region 83 occurs at radius r₁ and transition region 87 occursat radius r₃ for relative refractive index profile 80. Relativerefractive index profile 90 includes transition region 93 between aninner cladding region and an intermediate cladding region and transitionregion 97 between an intermediate cladding region and an outer claddingregion. Transition region 93 occurs at radius r₂ and transition region97 occurs at radius r₃ for relative refractive index profile 90.Relative refractive index profile 100 includes transition region 103between an inner cladding region and an intermediate cladding region andtransition region 107 between an intermediate cladding region and anouter cladding region. Transition region 103 occurs at radius r₂ andtransition region 107 occurs at radius r₃ for relative refractive indexprofile 100.

The effective areas A_(eff) associated with relative refractive indexprofiles 70, 80, 90, and 100 shown in FIG. 6 are 76 μm², 86 μm², 112μm², and 150 μm², respectively, at a wavelength of 1550 nm.

In one embodiment, the core region is a segmented core region with aninner core region surrounded by and directly adjacent to an outer coreregion, which is surrounded by and directly adjacent to the innercladding region (in embodiments with an inner cladding region) or anintermediate cladding region (in embodiments without an inner claddingregion). The outer core region has the radius r₁ and the inner coreregion has an outer radius r_(a) such that r_(a)<r₁. In one embodiment,each of the inner core region and outer core region has a relativerefractive index profile described by an α-profile. In one embodiment,the inner core region has an α value in the range from 1.5 to 10, or inthe range from 1.7 to 8.0, or in the range from 1.8 to 6.0, or in therange from 1.9 to 5.0, or in the range from 1.95 to 4.5, or in the rangefrom 2.0 to 4.0, or in the range from 4.0 to 9.5, or in the range from5.0 to 9.0, or in the range from 10 to 100, or in the range from 11 to40, or in the range from 12 to 30. In another embodiment, the inner coreregion has a relative refractive index profile described by an α-profileand the outer core region has a relative refractive index profiledescribed by a step-index profile. In another embodiment, the inner coreregion has a relative refractive index profile described by an α-profileand the outer core region has a relative refractive index profiledescribed by a rounded step-index profile.

In one embodiment, the inner core region is alkali-doped silica and theouter core region is halide-doped silica. Halide-doped silica includessilica doped with one or more of Cl, F, and Br. In one embodiment, theinner core region is silica doped with K₂O and the outer core region isdoped with F or a combination of F and Cl.

In embodiments in which each of the inner core region and outer coreregion has a relative refractive index profile described by anα-profile, the radius r_(a) is determined by minimizing the function χ²given in Eq. (10):

$\begin{matrix}{\chi^{2} = {{\sum\limits_{i = 1}^{a}\left\lbrack {{f\left( r_{i} \right)} - {\left( r_{a} \right)} - {\Delta \left( r_{i} \right)}} \right\rbrack^{2}} + {\sum\limits_{j = a}^{b}\left\lbrack {{\left( r_{j} \right)} - {\Delta \left( r_{j} \right)}} \right\rbrack^{2}}}} & (10)\end{matrix}$

where f(r_(i)) is an α-profile function for the inner core region,g(r_(j)) is an α-profile function for the outer core region, g(r_(a)) isthe value of g(r_(j)) at r_(j)=r_(a), Δ(r_(i)) is the measured relativerefractive index profile of the inner core region, A(r_(j)) is themeasured relative refractive index profile of the outer core region, theindex “i” indexes radial positions r_(i) in the inner core region, theindex “j” indexes radial positions r_(j) in the outer core region,0<r_(i)<r_(a), r_(a)≤r_(j)≤r_(b), the index “a” is the value of index“i” corresponding to r_(i)=r_(a), the index “b” is the value of index“j” corresponding to r_(j)=r_(i).

The effective area A_(eff) of the optical fibers disclosed herein isgreater than 70 μm², or greater than 80 μm², or greater than 90 μm², orgreater than 100 μm², or greater than 120 μm², or in the range from 70μm² to 160 μm², or in the range from 80 μm² to 120 μm², or in the rangefrom 90 μm² to 110 μm² at a wavelength of 1550 nm.

The attenuation of the optical fibers disclosed herein is less than orequal to 0.180 dB/km, or less than or equal to 0.175 dB/km, or less thanor equal to 0.170 dB/km, or less than or equal to 0.165 dB/km, or lessthan or equal to 0.160 dB/km at a wavelength of 1550 nm.

The mode field diameter of the optical fibers disclosed herein is in therange from 9.5 μm to 11.5 μm, or in the range from 9.75 μm to 11.25 μm,or in the range from 10.0 μm to 11.0 μm, at a wavelength of 1550 nm.

The cable cutoff wavelength λ_(CC) of the optical fibers disclosedherein is less than 1550 nm, or less than 1530 nm, or less than 1500 nm,or less than 1450 nm, or less than 1400 nm, or less than 1350 nm.

Optical Fiber Coatings. The transmissivity of light through an opticalfiber is highly dependent on the properties of the coatings applied tothe glass fiber. The coatings typically include a primary coating and asecondary coating, where the secondary coating surrounds the primarycoating and the primary coating contacts the glass fiber (which includesa central core region surrounded by a cladding region). The secondarycoating is a harder material (higher Young's modulus) than the primarycoating and is designed to protect the glass fiber from damage caused byabrasion or external forces that arise during processing, handling, andinstallation of the optical fiber. The primary coating is a softermaterial (lower Young's modulus) than the secondary coating and isdesigned to buffer or dissipates stresses that result from forcesapplied to the outer surface of the secondary coating. Dissipation ofstresses within the primary coating attenuates the stress and minimizesthe stress that reaches the glass fiber. The primary coating isespecially important in dissipating stresses that arise due to themicrobends that the optical fiber encounters when deployed in a cable.The microbending stresses transmitted to the glass fiber need to beminimized because microbending stresses create local perturbations inthe refractive index profile of the glass fiber. The local refractiveindex perturbations lead to intensity losses for the light transmittedthrough the glass fiber. By dissipating stresses, the primary coatingminimizes microbend-induced intensity losses

The primary coating 16 preferably has a higher refractive index than thecladding region of the glass fiber in order to allow it to strip errantoptical signals away from the core region. The primary coating shouldmaintain adequate adhesion to the glass fiber during thermal andhydrolytic aging, yet be strippable from the glass fiber for splicingpurposes.

Primary and secondary coatings are typically formed by applying acurable coating composition to the glass fiber as a viscous liquid andcuring. The optical fiber may also include a tertiary coating (notshown) that surrounds and is directly adjacent to the secondary coating.The tertiary coating may include pigments, inks or other coloring agentsto mark the optical fiber for identification purposes and typically hasa Young's modulus similar to the Young's modulus of the secondarycoating. The thickness of the tertiary coating is less than 10.0 μm, orless than 8.0 μm, or less than 6.0 μm, or less than 4.0 μm, or in therange from 1.0 μm to 10.0 μm, or in the range from 2.0 μm to 8.0 μm, inthe range from 3.0 μm to 6.0 μm.

Primary Coating Compositions. The primary coating is a cured product ofa curable primary coating composition. The curable primary coatingcompositions provide a primary coating for optical fibers that exhibitslow Young's modulus, low pullout force, and strong cohesion. The curableprimary coating compositions further enable formation of a primarycoating that features clean strippability and high resistance to defectformation during the stripping operation. Low pullout force facilitatesclean stripping of the primary coating with minimal residue and strongcohesion inhibits initiation and propagation of defects in the primarycoating when it is subjected to stripping forces. Even for opticalfibers with reduced primary coating thicknesses, the optical fibers areexpected to have low loss and low microbend loss performance. Theprimary coatings exhibit these advantages even at reduced thickness.

The primary coating is a cured product of a radiation-curable primarycoating composition that includes an oligomer, a monomer, aphotoinitiator and, optionally, an additive. The following disclosuredescribes oligomers for the radiation-curable primary coatingcompositions, radiation-curable primary coating compositions containingat least one of the oligomers, cured products of the radiation-curableprimary coating compositions that include at least one of the oligomers,glass fibers coated with a radiation-curable primary coating compositioncontaining at least one of the oligomers, and glass fibers coated withthe cured product of a radiation-curable primary coating compositioncontaining at least one of the oligomers.

The oligomer preferably includes a polyether urethane diacrylatecompound and a di-adduct compound. In one embodiment, the polyetherurethane diacrylate compound has a linear molecular structure. In oneembodiment, the oligomer is formed from a reaction between adiisocyanate compound, a polyol compound, and a hydroxy acrylatecompound, where the reaction produces a polyether urethane diacrylatecompound as a primary product (majority product) and a di-adductcompound as a byproduct (minority product). The reaction forms aurethane linkage upon reaction of an isocyanate group of thediisocyanate compound and an alcohol group of the polyol. The hydroxyacrylate compound reacts to quench residual isocyanate groups that arepresent in the composition formed from reaction of the diisocyanatecompound and polyol compound. As used herein, the term “quench” refersto conversion of isocyanate groups through a chemical reaction withhydroxyl groups of the hydroxy acrylate compound. Quenching of residualisocyanate groups with a hydroxy acrylate compound converts terminalisocyanate groups to terminal acrylate groups.

A preferred diisocyanate compound is represented by formula (I):

O═C═N—R₁—N═C═O  (I)

which includes two terminal isocyanate groups separated by a linkagegroup R₁. In one embodiment, the linkage group R₁ includes an alkylenegroup. The alkylene group of linkage group R₁ is linear (e.g. methyleneor ethylene), branched (e.g. isopropylene), or cyclic (e.g.cyclohexylene, phenylene). The cyclic group is aromatic or non-aromatic.In some embodiments, the linkage group R₁ is 4,4′-methylenebis(cyclohexyl) group and the diisocyanate compound is 4,4′-methylenebis(cyclohexyl isocyanate). In some embodiments, the linkage group R₁lacks an aromatic group, or lacks a phenylene group, or lacks anoxyphenylene group.

The polyol is represented by molecular formula (II):

where R₂ includes an alkylene group, —O—R₂— is a repeating alkoxylenegroup, and x is an integer. Preferably, x is greater than 20, or greaterthan 40, or greater than 50, or greater than 75, or greater than 100, orgreater than 125, or greater than 150, or in the range from 20 to 500,or in the range from 20 to 300, or in the range from 30 to 250, or inthe range from 40 to 200, or in the range from 60 to 180, or in therange from 70 to 160, or in the range from 80 to 140. R₂ is preferably alinear or branched alkylene group, such as methylene, ethylene,propylene (normal, iso or a combination thereof), or butylene (normal,iso, secondary, tertiary, or a combination thereof). The polyol may be apolyalkylene oxide, such as polyethylene oxide, or a polyalkyleneglycol, such as polypropylene glycol. Polypropylene glycol is apreferred polyol. The molecular weight of the polyol is greater than1000 g/mol, or greater than 2500 g/mol, or greater than 5000 g/mol, orgreater than 7500 g/mol, or greater than 10000 g/mol, or in the rangefrom 1000 g/mol to 20000 g/mol, or in the range from 2000 g/mol to 15000g/mol, or in the range from 2500 g/mol to 12500 g/mol, or in the rangefrom 2500 g/mol to 10000 g/mol, or in the range from 3000 g/mol to 7500g/mol, or in the range from 3000 g/mol to 6000 g/mol, or in the rangefrom 3500 g/mol to 5500 g/mol. In some embodiments, the polyol ispolydisperse and includes molecules spanning a range of molecularweights such that the totality of molecules combines to provide thenumber average molecular weight specified hereinabove.

The unsaturation of the polyol is less than 0.25 meq/g, or less than0.15 meq/g, or less than 0.10 meq/g, or less than 0.08 meq/g, or lessthan 0.06 meq/g, or less than 0.04 meq/g, or less than 0.02 meq/g, orless than 0.01 meq/g, or less than 0.005 meq/g, or in the range from0.001 meq/g to 0.15 meq/g, or in the range from 0.005 meq/g to 0.10meq/g, or in the range from 0.01 meq/g to 0.10 meq/g, or in the rangefrom 0.01 meq/g to 0.05 meq/g, or in the range from 0.02 meq/g to 0.10meq/g, or in the range from 0.02 meq/g to 0.05 meq/g. As used herein,unsaturation refers to the value determined by the standard methodreported in ASTM D4671-16. In the method, the polyol is reacted withmercuric acetate and methanol in a methanolic solution to produceacetoxymercuricmethoxy compounds and acetic acid. The reaction of thepolyol with mercuric acetate is equimolar and the amount of acetic acidreleased is determined by titration with alcoholic potassium hydroxideto provide the measure of unsaturation used herein. To preventinterference of excess mercuric acetate on the titration of acetic acid,sodium bromide is added to convert mercuric acetate to the bromide.

The reaction to form the oligomer further includes addition of a hydroxyacrylate compound to react with terminal isocyanate groups present inunreacted starting materials (e.g. the diisocyanate compound) orproducts formed in the reaction of the diisocyanate compound with thepolyol (e.g. urethane compounds with terminal isocyanate groups). Thehydroxy acrylate compound reacts with terminal isocyanate groups toprovide terminal acrylate groups for one or more constituents of theoligomer. In some embodiments, the hydroxy acrylate compound is presentin excess of the amount needed to fully convert terminal isocyanategroups to terminal acrylate groups. The oligomer includes a singlepolyether urethane acrylate compound or a combination of two or morepolyether urethane acrylate compounds.

The hydroxy acrylate compound is represented by molecular formula (III):

where R₃ includes an alkylene group. The alkylene group of R₃ is linear(e.g. methylene or ethylene), branched (e.g. isopropylene), or cyclic(e.g. phenylene). In some embodiments, the hydroxy acrylate compoundincludes substitution of the ethylenically unsaturated group of theacrylate group. Substituents of the ethylenically unsaturated groupinclude alkyl groups. An example of a hydroxy acrylate compound with asubstituted ethylenically unsaturated group is a hydroxy methacrylatecompound. The discussion that follows describes hydroxy acrylatecompounds. It should be understood, however, that the discussion appliesto substituted hydroxy acrylate compounds and in particular to hydroxymethacrylate compounds.

In different embodiments, the hydroxy acrylate compound is ahydroxyalkyl acrylate, such as 2-hydroxyethyl acrylate. The hydroxyacrylate compound may include water at residual or higher levels. Thepresence of water in the hydroxy acrylate compound may facilitatereaction of isocyanate groups to reduce the concentration of unreactedisocyanate groups in the final reaction composition. In variousembodiments, the water content of the hydroxy acrylate compound is atleast 300 ppm, or at least 600 ppm, or at least 1000 ppm, or at least1500 ppm, or at least 2000 ppm, or at least 2500 ppm.

In the foregoing exemplary molecular formulas (I), II), and (III), thegroups R₁, R₂, and R₃ independently are all the same, are all different,or include two groups that are the same and one group that is different.

The diisocyanate compound, hydroxy acrylate compound and polyol arecombined simultaneously and reacted, or are combined sequentially (inany order) and reacted. In one embodiment, the oligomer is formed byreacting a diisocyanate compound with a hydroxy acrylate compound andreacting the resulting product composition with a polyol. In anotherembodiment, the oligomer is formed by reacting a diisocyanate compoundwith a polyol compound and reacting the resulting product compositionwith a hydroxy acrylate compound.

The oligomer is formed from a reaction of a diisocyanate compound, ahydroxy acrylate compound, and a polyol, where the molar ratio of thediisocyanate compound to the hydroxy acrylate compound to the polyol inthe reaction process is n:m:p. n, m, and p are referred to herein asmole numbers or molar proportions of diisocyanate, hydroxy acrylate, andpolyol; respectively. The mole numbers n, m and p are positive integeror positive non-integer numbers. In embodiments, when p is 2.0, n is inthe range from 3.0 to 5.0, or in the range from 3.2 to 4.8, or in therange from 3.4 to 4.6, or in the range from 3.5 to 4.4, or in the rangefrom 3.6 to 4.2, or in the range from 3.7 to 4.0; and m is in the rangefrom 1.5 to 4.0, or in the range from 1.6 to 3.6, or in the range from1.7 to 3.2, or in the range from 1.8 to 2.8, or in the range from 1.9 to2.4. For values of p other than 2.0, the molar ratio n:m:p scalesproportionally. For example, the molar ratio n:m:p=4.0:3.0:2.0 isequivalent to the molar ratio n:m:p=2.0:1.5:1.0.

The mole number m may be selected to provide an amount of the hydroxyacrylate compound to stoichiometrically react with unreacted isocyanategroups present in the product composition formed from the reaction ofdiisocyanate compound and polyol used to form the oligomer. Theisocyanate groups may be present in unreacted diisocyanate compound(unreacted starting material) or in isocyanate-terminated urethanecompounds formed in reactions of the diisocyanate compound with thepolyol. Alternatively, the mole number m may be selected to provide anamount of the hydroxy acrylate compound in excess of the amount neededto stoichiometrically react with any unreacted isocyanate groups presentin the product composition formed from reaction of the diisocyanatecompound and the polyol. The hydroxy acrylate compound is added as asingle aliquot or multiple aliquots. In one embodiment, an initialaliquot of hydroxy acrylate is included in the reaction mixture used toform the oligomer and the product composition formed can be tested forthe presence of unreacted isocyanate groups (e.g. using FTIRspectroscopy to detect the presence of isocyanate groups). Additionalaliquots of hydroxy acrylate compound may be added to the productcomposition to stoichiometrically react with unreacted isocyanate groups(using, for example, FTIR spectroscopy to monitor a decrease in acharacteristic isocyanate frequency (e.g. at 2260 cm⁻¹ to 2270 cm⁻¹) asisocyanate groups are converted by the hydroxy acrylate compound). Inalternate embodiments, aliquots of hydroxy acrylate compound in excessof the amount needed to stoichiometrically react with unreactedisocyanate groups are added. As described more fully below, for a givenvalue of p, the ratio of the mole number m to the mole number ninfluences the relative proportions of polyether urethane diacrylatecompound and di-adduct compound in the oligomer and differences in therelative proportions of polyether urethane diacrylate compound anddi-adduct compound lead to differences in the tear strength and/orcritical stress of coatings formed from the oligomer.

In one embodiment, the oligomer is formed from a reaction mixture thatincludes 4,4′-methylene bis(cyclohexyl isocyanate), 2-hydroxyethylacrylate, and polypropylene glycol in the molar ratios n:m:p asspecified above, where the polypropylene glycol has a number averagemolecular weight in the range from 2500 g/mol to 6500 g/mol, or in therange from 3000 g/mol to 6000 g/mol, or in the range from 3500 g/mol to5500 g/mol.

The oligomer includes two components. The first component is a polyetherurethane diacrylate compound having the molecular formula (IV):

and the second component is a di-adduct compound having the molecularformula (V):

where the groups R₁, R₂, R₃, and the integer x are as describedhereinabove, y is a positive integer, and it is understood that thegroup R₁ in molecular formulas (IV) and (V) is the same as group R₁ inmolecular formula (I), the group R₂ in molecular formula (IV) is thesame as group R₂ in molecular formula (II), and the group R₃ inmolecular formulas (IV) and (V) is the same as group R₃ in molecularformula (III). The di-adduct compound corresponds to the compound formedby reaction of both terminal isocyanate groups of the diisocyanatecompound of molecular formula (I) with the hydroxy acrylate compound ofmolecular formula (II) where the diisocyanate compound has undergone noreaction with the polyol of molecular formula (II).

The di-adduct compound is formed from a reaction of the diisocyanatecompound with the hydroxy acrylate compound during the reaction used toform the oligomer. Alternatively, the di-adduct compound is formedindependent of the reaction used to form the oligomer and is added tothe product of the reaction used to form the polyether urethanediacrylate compound or to a purified form of the polyether urethanediacrylate compound. The hydroxy group of the hydroxy acrylate compoundreacts with an isocyanate group of the diisocyanate compound to providea terminal acrylate group. The reaction occurs at each isocyanate groupof the diisocyanate compound to form the di-adduct compound. Thedi-adduct compound is present in the oligomer in an amount of at least1.0 wt %, or at least 1.5 wt %, or at least 2.0 wt %, or at least 2.25wt %, or at least 2.5 wt %, or at least 3.0 wt %, or at least 3.5 wt %,or at least 4.0 wt %, or at least 4.5 wt %, or at least 5.0 wt %, or atleast 7.0 wt % or at least 9.0 wt %, or in the range from 1.0 wt % to10.0 wt %, or in the range from 2.0 wt % to 9.0 wt %, or in the rangefrom 2.5 wt % to 6.0 wt %, or in the range from 3.0 wt % to 8.0 wt %, orin the range from 3.0 wt % to 5.0 wt %, or in the range from 3.0 wt % to5.5 wt %, or in the range from 3.5 wt % to 5.0 wt %, or in the rangefrom 3.5 wt % to 7.0 wt %. It is noted that the concentration ofdi-adduct is expressed in terms of wt % of the oligomer and not in termsof wt % in the coating composition.

An illustrative reaction for synthesizing an oligomer in accordance withthe present disclosure includes reaction of a diisocyanate compound(4,4′-methylene bis(cyclohexyl isocyanate, which is also referred toherein as H12MDI) and a polyol (polypropylene glycol with M_(n)˜4000g/mol, which is also referred to herein as PPG4000) to form a polyetherurethane diisocyanate compound with formula (VI):

H12MDI˜PPG4000˜H12MDI˜PPG4000˜H12MDI  (VI)

where “˜” denotes a urethane linkage formed by the reaction of aterminal isocyanate group of H12MDI with a terminal alcohol group ofPPG4000; and ˜H12MDI, ˜H12MDI˜, and ˜PPG4000˜ refer to residues ofH12MDI and PPG4000 remaining after the reaction; and M_(n) refers tonumber average molecular weight. The polyether urethane diisocyanatecompound has a repeat unit of the type ˜(H12MDI˜PPG4000)˜. Theparticular polyether urethane diisocyanate shown includes two PPG4000units. The reaction may also provide products having one PPG4000 unit,or three or more PPG4000 units. The polyether urethane diisocyanate andany unreacted H12MDI include terminal isocyanate groups. In accordancewith the present disclosure, a hydroxy acrylate compound (such as2-hydroxyethyl acrylate, which is referred to herein as HEA) is includedin the reaction to react with terminal isocyanate groups to convert themto terminal acrylate groups. The conversion of terminal isocyanategroups to terminal acrylate groups effects a quenching of the isocyanategroup. The amount of HEA included in the reaction may be an amountestimated to react stoichiometrically with the expected concentration ofunreacted isocyanate groups or an amount in excess of the expectedstoichiometric amount. Reaction of HEA with the polyether urethanediisocyanate compound forms the polyether urethane acrylate compoundwith formula (VII):

HEA˜H12MDI˜PPG4000˜H12MDI˜PPG4000˜H12MDI  (VII)

and/or the polyether urethane diacrylate compound with formula (VIII):

HEA˜H12MDI˜PPG4000˜H12MDI˜PPG4000˜H12MDI˜HEA  (VIII)

and reaction of HEA with unreacted H12MDI forms the di-adduct compoundwith formula (IX):

HEA˜H12MDI˜HEA  (IX)

where, as above, ˜ designates a urethane linkage and ˜HEA designates theresidue of HEA remaining after reaction to form the urethane linkage(consistent with formulas (IV) and (V)). The combination of a polyetherurethane diacrylate compound and a di-adduct compound in the productcomposition constitutes an oligomer in accordance with the presentdisclosure. As described more fully hereinbelow, when one or moreoligomers are used in coating compositions, coatings having improvedtear strength and critical stress characteristics result. In particular,it is demonstrated that oligomers having a high proportion of di-adductcompound provide coatings with high tear strengths and/or high criticalstress values.

Although depicted for the illustrative combination of H12MDI, HEA andPPG4000, the foregoing reaction may be generalized to an arbitrarycombination of a diisocyanate compound, a hydroxy acrylate compound, anda polyol, where the hydroxy acrylate compound reacts with terminalisocyanate groups to form terminal acrylate groups and where urethanelinkages form from reactions of isocyanate groups and alcohol groups ofthe polyol or hydroxy acrylate compound.

The oligomer includes a compound that is a polyether urethane diacrylatecompound with formula (X):

(hydroxy acrylate)˜(diisocyanate˜polyol)_(x)˜diisocyanate˜(hydroxyacrylate)  (X)

and a compound that is a di-adduct compound with formula (XI):

(hydroxy acrylate)˜diisocyanate˜(hydroxy acrylate)  (XI)

where the relative proportions of diisocyanate compound, hydroxyacrylate compound, and polyol used in the reaction to form the oligomercorrespond to the mole numbers n, m, and p disclosed hereinabove.

Compounds represented by molecular formulas (I) and (II) above, forexample, react to form a polyether urethane diisocyanate compoundrepresented by molecular formula (XII):

where y is the same as y in formula (IV) and is 1, or 2, or 3 or 4 orhigher; and x is determined by the number of repeat units of the polyol(as described hereinabove).

Further reaction of the polyether urethane isocyanate of molecularformula (VI) with the hydroxy acrylate of molecular formula (III)provides the polyether urethane diacrylate compound represented bymolecular formula (IV) referred to hereinabove and repeated below:

where y is 1, or 2, or 3, or 4 or higher; and x is determined by thenumber of repeat units of the polyol (as described hereinabove).

In an embodiment, the reaction between the diisocyanate compound,hydroxy acrylate compound, and polyol yields a series of polyetherurethane diacrylate compounds that differ in y such that the averagevalue of y over the distribution of compounds present in the finalreaction mixture is a non-integer. In an embodiment, the average valueof y in the polyether urethane diisocyanates and polyether urethanediacrylates of molecular formulas (VI) and (IV) corresponds to p or p−1(where p is as defined hereinabove). In an embodiment, the averagenumber of occurrences of the group R₁ in the polyether urethanediisocyanates and polyether urethane diacrylates of the molecularformulas (XII) and (IV) correspond to n (where n is as definedhereinabove).

The relative proportions of the polyether urethane diacrylate anddi-adduct compounds produced in the reaction are controlled by varyingthe molar ratio of the mole numbers n, m, and p. By way of illustration,the case where p=2.0 is considered. In the theoretical limit of completereaction, two equivalents p of polyol would react with three equivalentsn of a diisocyanate to form a compound having molecular formula (VI) inwhich y=2. The compound includes two terminal isocyanate groups, whichcan be quenched with subsequent addition of two equivalents m of ahydroxy acrylate compound in the theoretical limit to form thecorresponding polyether urethane diacrylate compound (IV) with y=2. Atheoretical molar ratio n:m:p=3.0:2.0:2.0 is defined for this situation.

In the foregoing exemplary theoretical limit, a reaction ofdiisocyanate, hydroxy acrylate, and polyol in the theoretical molarratio n:m:p=3.0:2.0:2.0 provides a polyether urethane diacrylatecompound having molecular formula (IV) in which y=2 without forming adi-adduct compound. Variations in the mole numbers n, m, and p providecontrol over the relative proportions of polyether urethane diacrylateand di-adduct formed in the reaction. Increasing the mole number nrelative to the mole number m or the mole number p, for example, mayincrease the amount of di-adduct compound formed in the reaction.Reaction of the diisocyanate compound, the hydroxy acrylate compound,and polyol compound in molar ratios n:m:p, where n is in the range from3.0 to 5.0, m is in the range within ±15% of 2n−4 or within ±10% of 2n−4or within ±5% of 2n−4, and p is 2.0, for example, produce amounts of thedi-adduct compound in the oligomer sufficient to achieve the preferredprimary coating properties. By way of example, the embodiment in whichn=4.0, m is within ±15% of 2n−4, and p=2.0 means that n=4.0, m is within±15% of 4, and p=2.0, which means that that n=4.0, m is in the rangefrom 3.4 to 4.6, and p=2.0.

Variations in the relative proportions of di-adduct and polyetherurethane diacrylate are obtained through changes in the mole numbers n,m, and p and through such variations, it is possible to preciselycontrol the Young's modulus, in situ modulus, tear strength, criticalstress, tensile toughness, and other mechanical properties of coatingsformed from coating compositions that include the oligomer. In oneembodiment, control over properties is achievable by varying the numberof units of polyol in the polyether urethane diacrylate compound (e.g.p=2.0 vs. p=3.0 vs. p=4.0). In another embodiment, control of tearstrength, tensile toughness, and other mechanical properties is achievedby varying the proportions polyether urethane diacrylate compound anddi-adduct compound. For a polyether urethane compound with a givennumber of polyol units, oligomers having variable proportions ofdi-adduct compound can be prepared. The variability in proportion ofdi-adduct compound can be finely controlled to provide oligomers basedon a polyether urethane diacrylate compound with a fixed number ofpolyol units that provide coatings that offer precise or targeted valuesof tear strength, critical stress, tensile toughness, or othermechanical properties.

Improved fiber primary coatings result when utilizing a primary coatingcomposition that incorporates an oligomer that includes a polyetherurethane acrylate compound represented by molecular formula (IV) and adi-adduct compound represented by molecular formula (V), whereconcentration of the di-adduct compound in the oligomer is at least 1.0wt %, or at least 1.5 wt %, or at least 2.0 wt %, or at least 2.25 wt %,or at least 2.5 wt %, or at least 3.0 wt %, or at least 3.5 wt %, or atleast 4.0 wt %, or at least 4.5 wt %, or at least 5.0 wt %, or at least7.0 wt % or at least 9.0 wt %, or in the range from 1.0 wt % to 10.0 wt%, or in the range from 2.0 wt % to 9.0 wt %, or in the range from 3.0wt % to 8.0 wt %, or in the range from 3.5 wt % to 7.0 wt % or in therange from 2.5 wt % to 6.0 wt %, or in the range from 3.0 wt % to 5.5 wt%, or in the range from 3.5 wt % to 5.0 wt %. It is noted that theconcentration of di-adduct is expressed in terms of wt % of the oligomerand not in terms of wt % in the coating composition. The concentrationof the di-adduct compound is increased in one embodiment by varying themolar ratio n:m:p of diisocyanate:hydroxy acrylate:polyol. In oneaspect, molar ratios n:m:p that are rich in diisocyanate relative topolyol promote the formation of the di-adduct compound.

In the exemplary stoichiometric ratio n:m:p=3:2:2 described hereinabove,the reaction proceeds with p equivalents of polyol, n=p+1 equivalents ofdiisocyanate, and two equivalents of hydroxy acrylate. If the molenumber n exceeds p+1, the diisocyanate compound is present in excessrelative to the amount of polyol compound needed to form the polyetherurethane acrylate of molecular formula (IV). The presence of excessdiisocyanate shifts the distribution of reaction products towardenhanced formation of the di-adduct compound.

To promote formation of the di-adduct compound from excess diisocyanatecompound, the amount of hydroxy acrylate can also be increased. For eachequivalent of diisocyanate above the stoichiometric mole number n=p+1,two equivalents of hydroxy acrylate are needed to form the di-adductcompound. In the case of arbitrary mole number p (polyol), thestoichiometric mole numbers n (diisocyanate) and m (hydroxy acrylate)are p+1 and 2, respectively. As the mole number n is increased above thestoichiometric value, the equivalents of hydroxy acrylate needed forcomplete reaction of excess diisocyanate to form the di-adduct compoundmay be expressed as m=2+2[n−(p+1)], where the leading term “2”represents the equivalents of hydroxy acrylate needed to terminate thepolyether urethane acrylate compound (compound having molecular formula(V)) and the term 2[n−(p+1)] represents the equivalents of hydroxyacrylate needed to convert the excess starting diisocyanate to thedi-adduct compound. If the actual value of the mole number m is lessthan this number of equivalents, the available hydroxy acrylate reactswith isocyanate groups present on the oligomer or free diisocyanatemolecules to form terminal acrylate groups. The relative kinetics of thetwo reaction pathways dictates the relative amounts of polyetherurethane diacrylate and di-adduct compounds formed and the deficit inhydroxy acrylate relative to the amount required to quench all unreactedisocyanate groups may be controlled to further influence the relativeproportions of polyether urethane diacrylate and di-adduct formed in thereaction.

In some embodiments, the reaction includes heating the reactioncomposition formed from the diisocyanate compound, hydroxy acrylatecompound, and polyol. The heating facilitates conversion of terminalisocyanate groups to terminal acrylate groups through a reaction of thehydroxy acrylate compound with terminal isocyanate groups. In differentembodiments, the hydroxy acrylate compound is present in excess in theinitial reaction mixture and/or is otherwise available or added inunreacted form to effect conversion of terminal isocyanate groups toterminal acrylate groups. The heating occurs at a temperature above 40°C. for at least 12 hours, or at a temperature above 40° C. for at least18 hours, or at a temperature above 40° C. for at least 24 hours, or ata temperature above 50° C. for at least 12 hours, or at a temperatureabove 50° C. for at least 18 hours, or at a temperature above 50° C. forat least 24 hours, or at a temperature above 60° C. for at least 12hours, or at a temperature above 60° C. for at least 18 hours, or at atemperature above 60° C. for at least 24 hours.

In an embodiment, conversion of terminal isocyanate groups on thepolyether urethane diacrylate compound or starting diisocyanate compound(unreacted initial amount or amount present in excess) to terminalacrylate groups is facilitated by the addition of a supplemental amountof hydroxy acrylate compound to the reaction mixture. As indicatedhereinabove, the amount of hydroxy acrylate compound needed to quench(neutralize) terminal isocyanate groups may deviate from the theoreticalnumber of equivalents due, for example, to incomplete reaction or adesire to control the relative proportions of polyether urethanediacrylate compound and di-adduct compound. As described hereinabove,once the reaction has proceeded to completion or other endpoint, it ispreferable to quench (neutralize) residual isocyanate groups to providea stabilized reaction product. In an embodiment, supplemental hydroxyacrylate is added to accomplish this objective.

In an embodiment, the amount of supplemental hydroxy acrylate compoundis in addition to the amount included in the initial reaction process.The presence of terminal isocyanate groups at any stage of the reactionis monitored, for example, by FTIR spectroscopy (e.g. using acharacteristic isocyanate stretching mode near 2265 cm′) andsupplemental hydroxy acrylate compound is added as needed until theintensity of the characteristic stretching mode of isocyanate groups isnegligible or below a pre-determined threshold. In an embodiment,supplemental hydroxy acrylate compound is added beyond the amount neededto fully convert terminal isocyanate groups to terminal acrylate groups.In different embodiments, supplemental hydroxy acrylate compound isincluded in the initial reaction mixture (as an amount above thetheoretical amount expected from the molar amounts of diisocyanate andpolyol), added as the reaction progresses, and/or added after reactionof the diisocyanate and polyol compounds has occurred to completion orpre-determined extent.

Amounts of hydroxy acrylate compound above the amount needed to fullyconvert isocyanate groups are referred to herein as excess amounts ofhydroxy acrylate compound. When added, the excess amount of hydroxyacrylate compound is at least 20% of the amount of supplemental hydroxyacrylate compound needed to fully convert terminal isocyanate groups toterminal acrylate groups, or at least 40% of the amount of supplementalhydroxy acrylate compound needed to fully convert terminal isocyanategroups to terminal acrylate groups, or at least 60% of the amount ofsupplemental hydroxy acrylate compound needed to fully convert terminalisocyanate groups to terminal acrylate groups, or at least 90% of theamount of supplemental hydroxy acrylate compound needed to fully convertterminal isocyanate groups to terminal acrylate groups.

In an embodiment, the amount of supplemental hydroxy acrylate compoundmay be sufficient to completely or nearly completely quench residualisocyanate groups present in the oligomer formed in the reaction.Quenching of isocyanate groups is desirable because isocyanate groupsare relatively unstable and often undergo reaction over time. Suchreaction alters the characteristics of the reaction composition oroligomer and may lead to inconsistencies in coatings formed therefrom.Reaction compositions and products formed from the starting diisocyanateand polyol compounds that are free of residual isocyanate groups areexpected to have greater stability and predictability ofcharacteristics.

The oligomer of the primary coating composition includes a polyetherurethane diacrylate compound and di-adduct compound as describedhereinabove. In some embodiments, the oligomer includes two or morepolyether urethane diacrylate compounds and/or two or more di-adductcompounds. The oligomer content of the primary coating compositionincludes the combined amounts of the one or more polyether urethanediacrylate compound(s) and one or more di-adduct compound(s) and isgreater than 20 wt %, or greater than 30 wt %, or greater than 40 wt %,or in the range from 20 wt % to 80 wt %, or in the range from 30 wt % to70 wt %, or in the range from 40 wt % to 60 wt %, where theconcentration of di-adduct compound within the oligomer content is asdescribed above.

The curable primary coating composition further includes one or moremonomers. The one or more monomers is/are selected to be compatible withthe oligomer, to control the viscosity of the primary coatingcomposition to facilitate processing, and/or to influence the physicalor chemical properties of the coating formed as the cured product of theprimary coating composition. The monomers include radiation-curablemonomers such as ethylenically-unsaturated compounds, ethoxylatedacrylates, ethoxylated alkylphenol monoacrylates, propylene oxideacrylates, n-propylene oxide acrylates, isopropylene oxide acrylates,monofunctional acrylates, monofunctional aliphatic epoxy acrylates,multifunctional acrylates, multifunctional aliphatic epoxy acrylates,and combinations thereof.

Representative radiation-curable ethylenically unsaturated monomersinclude alkoxylated monomers with one or more acrylate or methacrylategroups. An alkoxylated monomer is one that includes one or morealkoxylene groups, where an alkoxylene group has the form —O—R— and R isa linear or branched alkylene group. Examples of alkoxylene groupsinclude ethoxylene (—O—CH₂—CH₂—), n-propoxylene (—O—CH₂—CH₂—CH₂—),isopropoxylene (—O—CH₂—CH(CH₃)—, or —O—CH(CH₃)—CH₂—), etc. As usedherein, the degree of alkoxylation refers to the number of alkoxylenegroups in the monomer. In one embodiment, the alkoxylene groups arebonded consecutively in the monomer.

In some embodiments, the primary coating composition includes analkoxylated monomer of the form R₄—R₅—O—(CH(CH₃)CH₂—O)_(q)—C(O)CH═CH₂,where R₄ and R₅ are aliphatic, aromatic, or a mixture of both, and q=1to 10, or R₄—O—(CH(CH₃)CH₂—O)_(q)—C(O)CH═CH₂, where C(O) is a carbonylgroup, R₁ is aliphatic or aromatic, and q=1 to 10.

Representative examples of monomers include ethylenically unsaturatedmonomers such as lauryl acrylate (e.g., SR335 available from SartomerCompany, Inc., AGEFLEX FA12 available from BASF, and PHOTOMER 4812available from IGM Resins), ethoxylated nonylphenol acrylate (e.g.,SR504 available from Sartomer Company, Inc. and PHOTOMER 4066 availablefrom IGM Resins), caprolactone acrylate (e.g., SR495 available fromSartomer Company, Inc., and TONE M-100 available from Dow Chemical),phenoxyethyl acrylate (e.g., SR339 available from Sartomer Company,Inc., AGEFLEX PEA available from BASF, and PHOTOMER 4035 available fromIGM Resins), isooctyl acrylate (e.g., SR440 available from SartomerCompany, Inc. and AGEFLEX FA8 available from BASF), tridecyl acrylate(e.g., SR489 available from Sartomer Company, Inc.), isobornyl acrylate(e.g., SR506 available from Sartomer Company, Inc. and AGEFLEX IBOAavailable from CPS Chemical Co.), tetrahydrofurfuryl acrylate (e.g.,SR285 available from Sartomer Company, Inc.), stearyl acrylate (e.g.,SR257 available from Sartomer Company, Inc.), isodecyl acrylate (e.g.,SR395 available from Sartomer Company, Inc. and AGEFLEX FA10 availablefrom BASF), 2-(2-ethoxyethoxy)ethyl acrylate (e.g., SR256 available fromSartomer Company, Inc.), epoxy acrylate (e.g., CN120, available fromSartomer Company, and EBECRYL 3201 and 3604, available from CytecIndustries Inc.), lauryloxyglycidyl acrylate (e.g., CN130 available fromSartomer Company) and phenoxyglycidyl acrylate (e.g., CN131 availablefrom Sartomer Company) and combinations thereof.

In some embodiments, the monomer component of the primary coatingcomposition includes a multifunctional (meth)acrylate. Multifunctionalethylenically unsaturated monomers include multifunctional acrylatemonomers and multifunctional methacrylate monomers. Multifunctionalacrylates are acrylates having two or more polymerizable acrylatemoieties per molecule, or three or more polymerizable acrylate moietiesper molecule. Examples of multifunctional (meth)acrylates includedipentaerythritol monohydroxy pentaacrylate (e.g., PHOTOMER 4399available from IGM Resins); methylolpropane polyacrylates with andwithout alkoxylation such as trimethylolpropane triacrylate,ditrimethylolpropane tetraacrylate (e.g., PHOTOMER 4355, IGM Resins);alkoxylated glyceryl triacrylates such as propoxylated glyceryltriacrylate with propoxylation being 3 or greater (e.g., PHOTOMER 4096,IGM Resins); and erythritol polyacrylates with and without alkoxylation,such as pentaerythritol tetraacrylate (e.g., SR295, available fromSartomer Company, Inc. (Westchester, Pa.)), ethoxylated pentaerythritoltetraacrylate (e.g., SR494, Sartomer Company, Inc.), dipentaerythritolpentaacrylate (e.g., PHOTOMER 4399, IGM Resins, and SR399, SartomerCompany, Inc.), tripropyleneglycol diacrylate, propoxylated hexanedioldiacrylate, tetrapropyleneglycol diacrylate, pentapropyleneglycoldiacrylate, methacrylate analogs of the foregoing, and combinationsthereof.

In some embodiments, the primary coating composition includes an N-vinylamide monomer such as an N-vinyl lactam, or N-vinyl pyrrolidinone, orN-vinyl caprolactam, where the N-vinyl amide monomer is present in thecoating composition at a concentration greater than 1.0 wt %, or greaterthan 2.0 wt %, or greater than 3.0 wt %, or in the range from 1.0 wt %to 15.0 wt %, or in the range from 2.0 wt % to 10.0 wt %, or in therange from 3.0 wt % to 8.0 wt %.

In an embodiment, the primary coating composition includes one or moremonofunctional acrylate or methacrylate monomers in an amount from 15 wt% to 90 wt %, or from 30 wt % to 75 wt %, or from 40 wt % to 65 wt %. Inanother embodiment, the primary coating composition may include one ormore monofunctional aliphatic epoxy acrylate or methacrylate monomers inan amount from 5 wt % to 40 wt %, or from 10 wt % to 30 wt %.

In an embodiment, the monomer component of the primary coatingcomposition includes a hydroxyfunctional monomer. A hydroxyfunctionalmonomer is a monomer that has a pendant hydroxy moiety in addition toother reactive functionality such as (meth)acrylate. Examples ofhydroxyfunctional monomers including pendant hydroxyl groups includecaprolactone acrylate (available from Dow Chemical as TONE M-100);poly(alkylene glycol) mono(meth)acrylates, such as poly(ethylene glycol)monoacrylate, poly(propylene glycol) monoacrylate, andpoly(tetramethylene glycol) monoacrylate (each available from Monomer,Polymer & Dajac Labs); 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl(meth)acrylate, and 4-hydroxybutyl (meth)acrylate (each available fromAldrich).

In an embodiment, the hydroxyfunctional monomer is present in an amountsufficient to improve adhesion of the primary coating to the opticalfiber. The hydroxyfunctional monomer is present in the coatingcomposition in an amount between about 0.1 wt % and about 25 wt %, or inan amount between about 5 wt % and about 8 wt %. The use of thehydroxyfunctional monomer may decrease the amount of adhesion promoternecessary for adequate adhesion of the primary coating to the opticalfiber. The use of the hydroxyfunctional monomer may also tend toincrease the hydrophilicity of the coating. Hydroxyfunctional monomersare described in more detail in U.S. Pat. No. 6,563,996, the disclosureof which is hereby incorporated by reference in its entirety.

In different embodiments, the total monomer content of the primarycoating composition is between about 15 wt % and about 90 wt %, orbetween about 30 wt % and about 75 wt %, or between about 40 wt % andabout 65 wt %.

In addition to a curable monomer and a curable oligomer, the curableprimary coating composition also includes a polymerization initiator.The polymerization initiator facilitates initiation of thepolymerization process associated with the curing of the coatingcomposition to form the coating. Polymerization initiators includethermal initiators, chemical initiators, electron beam initiators, andphotoinitiators. Photoinitiators include ketonic photoinitiators and/orphosphine oxide photoinitiators. When used in the curing of the coatingcomposition, the photoinitiator is present in an amount sufficient toenable rapid radiation curing.

Representative photoinitiators include 1-hydroxycyclohexylphenyl ketone(e.g., IRGACURE 184 available from BASF));bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (e.g.,commercial blends IRGACURE 1800, 1850, and 1700 available from BASF);2,2-dimethoxy-2-phenylacetophenone (e.g., IRGACURE 651, available fromBASF); bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (IRGACURE 819);(2,4,6-trimethylbenzoyl)diphenyl phosphine oxide (LUCIRIN TPO, availablefrom BASF (Munich, Germany));ethoxy(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (LUCIRIN TPO-L fromBASF); and combinations thereof.

The coating composition includes a single photoinitiator or acombination of two or more photoinitiators. The total photoinitiatorcontent of the coating composition is up to about 10 wt %, or betweenabout 0.5 wt % and about 6 wt %.

The curable primary coating composition optionally includes one or moreadditives. Additives include an adhesion promoter, a strength additive,an antioxidant, a catalyst, a stabilizer, an optical brightener, aproperty-enhancing additive, an amine synergist, a wax, a lubricant,and/or a slip agent. Some additives operate to control thepolymerization process, thereby affecting the physical properties (e.g.,modulus, glass transition temperature) of the polymerization productformed from the coating composition. Other additives affect theintegrity of the cured product of the primary coating composition (e.g.,protect against de-polymerization or oxidative degradation).

An adhesion promoter is a compound that facilitates adhesion of theprimary coating and/or primary composition to glass (e.g. the claddingportion of a glass fiber). Suitable adhesion promoters includealkoxysilanes, mercapto-functional silanes, organotitanates, andzirconates. Representative adhesion promoters include mercaptoalkylsilanes or mercaptoalkoxy silanes such as3-mercaptopropyl-trialkoxysilane (e.g.,3-mercaptopropyl-trimethoxysilane, available from Gelest (Tullytown,Pa.)); bis(trialkoxysilyl-ethyl)benzene; acryloxypropyltrialkoxysilane(e.g., (3-acryloxypropyl)-trimethoxysilane, available from Gelest),methacryloxypropyltrialkoxysilane, vinyltrialkoxysilane,bis(trialkoxysilylethyl)hexane, allyltrialkoxysilane,styrylethyltrialkoxysilane, and bis(trimethoxysilylethyl)benzene(available from United Chemical Technologies (Bristol, Pa.)); see U.S.Pat. No. 6,316,516, the disclosure of which is hereby incorporated byreference in its entirety herein.

The adhesion promoter is present in the primary coating composition inan amount between 0.02 wt % and 10.0 wt %, or between 0.05 wt % and 4.0wt %, or between 0.1 wt % and 4.0 wt %, or between 0.1 wt % and 3.0 wt%, or between 0.1 wt % and 2.0 wt %, or between 0.1 wt % and 1.0 wt %,or between 0.5 wt % and 4.0 wt %, or between 0.5 wt % and 3.0 wt %, orbetween 0.5 wt % and 2.0 wt %, or between 0.5 wt % and 1.0 wt %.

A representative antioxidant is thiodiethylenebis[3-(3,5-di-tert-butyl)-4-hydroxy-phenyl) propionate] (e.g., IRGANOX1035, available from BASF). In some aspects, an antioxidant is presentin the coating composition in an amount greater than 0.25 wt %, orgreater than 0.50 wt %, or greater than 0.75 wt %, or greater than 1.0wt %, or an amount in the range from 0.25 wt % to 3.0 wt %, or an amountin the range from 0.50 wt % to 2.0 wt %, or an amount in the range from0.75 wt % to 1.5 wt %.

Representative optical brighteners include TINOPAL OB (available fromBASF); Blankophor KLA (available from Bayer); bisbenzoxazole compounds;phenylcoumarin compounds; and bis(styryl)biphenyl compounds. In anembodiment, the optical brightener is present in the coating compositionat a concentration of 0.005 wt % to 0.3 wt %.

Representative amine synergists include triethanolamine;1,4-diazabicyclo[2.2.2]octane (DABCO), triethylamine, andmethyldiethanolamine. In an embodiment, an amine synergist is present ata concentration of 0.02 wt % to 0.5 wt %.

Primary Coating—Properties. Relevant properties of the primary coatinginclude radius, thickness, Young's modulus, and in situ modulus.

The radius r₅ of the primary coating is less than or equal to 85.0 μm,or less than or equal to 80.0 μm, or less than or equal to 75.0 μm, orless than or equal to 70.0 μm, or in the range from 57.5 μm to 92.5 μm,or in the range from 60.0 μm to 90.0 μm, or in the range from 62.5 μm to87.5 μm, or in the range from 65.0 μm to 85.0 μm, or in the range from67.5 μm to 82.5 μm.

To facilitate decreases in the diameter of the optical fiber, it ispreferable to minimize the thickness r₅−r₄ of the primary coating. Thethickness r₅−r₄ of the primary coating is in the range from 20.0 μm to45.0 μm, or in the range from 20.0 μm to 42.5 μm, or in the range from20.0 μm to 40.0 μm, or in the range from 20.0 μm to 37.5 μm, or in therange from 20.0 μm to 35.0 μm, or in the range from 22.5 μm to 45.0 μm,or in the range from 22.5 μm to 42.5 μm, or in the range from 22.5 μm to40.0 μm, or in the range from 22.5 μm to 37.5 μm, or in the range from22.5 μm to 35.0 μm, or in the range from 25.0 μm to 45.0 μm, or in therange from 25.0 μm to 42.5 μm, or in the range from 25.0 μm to 40.0 μm,or in the range from 25.0 μm to 37.5 μm, or in the range from 25.0 μm to35.0 μm.

To facilitate effective buffering of stress and protection of the glassfiber, it is preferable for the primary coating to have a low Young'smodulus and/or a low in situ modulus. The Young's modulus of the primarycoating is less than or equal to 0.7 MPa, or less than or equal to 0.6MPa, or less than or equal to 0.5 MPa, or less than or equal to 0.4 MPa,or less than or equal to 0.3 MPa, or in the range from 0.2 MPa to 0.7MPa, or in the range from 0.3 MPa to 0.6 MPa. The in situ modulus of theprimary coating is less than or equal to 0.40 MPa, or less than or equalto 0.35 MPa, or less than or equal to 0.30 MPa, or less than or equal to0.25 MPa, or less than or equal to 0.20 MPa, or less than or equal to0.15 MPa, or less than or equal to 0.10 MPa, or in the range from 0.05MPa to 0.40 MPa, or in the range from 0.05 MPa to 0.30 MPa, or in therange from 0.05 MPa to 0.25 MPa, or in the range from 0.10 MPa to 0.25MPa.

Secondary Coating—Compositions. The secondary coating is a cured productof a curable secondary coating composition that includes a monomer, aphotoinitiator, an optional oligomer, and an optional additive. Thepresent disclosure describes optional oligomers for theradiation-curable secondary coating compositions, radiation-curablesecondary coating compositions, cured products of the radiation-curablesecondary coating compositions, optical fibers coated with aradiation-curable secondary coating composition, and optical fiberscoated with the cured product of a radiation-curable secondary coatingcomposition.

The secondary coating is formed as the cured product of aradiation-curable secondary coating composition that includes a monomercomponent with one or more monomers. The monomers preferably includeethylenically unsaturated compounds. The one or more monomers may bepresent in an amount of 50 wt % or greater, or in an amount from about60 wt % to about 99 wt %, or in an amount from about 75 wt % to about 99wt %, or in an amount from about 80 wt % to about 99 wt % or in anamount from about 85 wt % to about 99 wt %. In one embodiment, thesecondary coating is the radiation-cured product of a secondary coatingcomposition that contains urethane acrylate monomers.

The monomers include functional groups that are polymerizable groupsand/or groups that facilitate or enable crosslinking. The monomers aremonofunctional monomers or multifunctional monomers. In combinations oftwo or more monomers, the constituent monomers are monofunctionalmonomers, multifunctional monomers, or a combination of monofunctionalmonomers and multifunctional monomers. In one embodiment, the monomercomponent of the curable secondary coating composition includesethylenically unsaturated monomers. Suitable functional groups forethylenically unsaturated monomers include, without limitation,(meth)acrylates, acrylamides, N-vinyl amides, styrene and substitutedstyrene, vinyl ethers, vinyl esters, acid esters, and combinationsthereof.

In one embodiment, the monomer component of the curable secondarycoating composition includes ethylenically unsaturated monomers. Themonomers include functional groups that are polymerizable groups and/orgroups that facilitate or enable crosslinking. The monomers aremonofunctional monomers or multifunctional monomers. In combinations oftwo or more monomers, the constituent monomers are monofunctionalmonomers, multifunctional monomers, or a combination of monofunctionalmonomers and multifunctional monomers. Suitable functional groups forethylenically unsaturated monomers include, without limitation,(meth)acrylates, acrylamides, N-vinyl amides, styrene and substitutedstyrene, vinyl ethers, vinyl esters, acid esters, and combinationsthereof.

Exemplary monofunctional ethylenically unsaturated monomers for thecurable secondary coating composition include, without limitation,hydroxyalkyl acrylates such as 2-hydroxyethyl-acrylate,2-hydroxypropyl-acrylate, and 2-hydroxybutyl-acrylate; long- andshort-chain alkyl acrylates such as methyl acrylate, ethyl acrylate,propyl acrylate, isopropyl acrylate, butyl acrylate, amyl acrylate,isobutyl acrylate, t-butyl acrylate, pentyl acrylate, isoamyl acrylate,hexyl acrylate, heptyl acrylate, octyl acrylate, isooctyl acrylate,2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, isodecylacrylate, undecyl acrylate, dodecyl acrylate, lauryl acrylate, octadecylacrylate, and stearyl acrylate; aminoalkyl acrylates such asdimethylaminoethyl acrylate, diethylaminoethyl acrylate, and7-amino-3,7-dimethyloctyl acrylate; alkoxyalkyl acrylates such asbutoxyethyl acrylate, phenoxyethyl acrylate (e.g., SR339, SartomerCompany, Inc.), and ethoxyethoxyethyl acrylate; single and multi-ringcyclic aromatic or non-aromatic acrylates such as cyclohexyl acrylate,benzyl acrylate, dicyclopentadiene acrylate, dicyclopentanyl acrylate,tricyclodecanyl acrylate, bomyl acrylate, isobornyl acrylate (e.g.,SR423, Sartomer Company, Inc.), tetrahydrofiurfuryl acrylate (e.g.,SR285, Sartomer Company, Inc.), caprolactone acrylate (e.g., SR495,Sartomer Company, Inc.), and acryloylmorpholine; alcohol-based acrylatessuch as polyethylene glycol monoacrylate, polypropylene glycolmonoacrylate, methoxyethylene glycol acrylate, methoxypolypropyleneglycol acrylate, methoxypolyethylene glycol acrylate, ethoxydiethyleneglycol acrylate, and various alkoxylated alkylphenol acrylates such asethoxylated(4) nonylphenol acrylate (e.g., Photomer 4066, IGM Resins);acrylamides such as diacetone acrylamide, isobutoxymethyl acrylamide,N,N′-dimethyl-aminopropyl acrylamide, N,N-dimethyl acrylamide, N,Ndiethyl acrylamide, and t-octyl acrylamide; vinylic compounds such asN-vinylpyrrolidone and N-vinylcaprolactam; and acid esters such asmaleic acid ester and fumaric acid ester. With respect to the long andshort chain alkyl acrylates listed above, a short chain alkyl acrylateis an alkyl group with 6 or less carbons and a long chain alkyl acrylateis an alkyl group with 7 or more carbons.

Representative radiation-curable ethylenically unsaturated monomersincluded alkoxylated monomers with one or more acrylate or methacrylategroups. An alkoxylated monomer is one that includes one or morealkoxylene groups, where an alkoxylene group has the form —O—R— and R isa linear or branched hydrocarbon. Examples of alkoxylene groups includeethoxylene (—O—CH₂—CH₂—), n-propoxylene (—O—CH₂—CH₂—CH₂—),isopropoxylene (—O—CH₂—CH(CH₃)—), etc. As used herein, the degree ofalkoxylation refers to the number of alkoxylene groups in the monomer.In one embodiment, the alkoxylene groups are bonded consecutively in themonomer.

As used herein, degree of alkoxylation refers to the number ofalkoxylene groups divided by the number of acrylate and methacrylategroups in a molecule of the monomer. For monofunctional alkoxylatedmonomers, the degree of alkoxylation corresponds to the number ofalkoxylene groups in a molecule of the monomer. In a preferredembodiment, the alkoxylene groups of a monofunctional alkoxylatedmonomer are bonded consecutively. For a difunctional alkoxylatedmonomer, the degree of alkoxylation corresponds to one half of thenumber of alkoxylene groups in a molecule of the monomer. In a preferredembodiment, the alkoxylene groups in a difunctional alkoxylated monomerare bonded consecutively in each of two groups where the two groups areseparated by a chemical linkage and each group includes half orapproximately half of the number of alkoxylene groups in the molecule.For a trifunctional alkoxylated monomer, the degree of alkoxylationcorresponds to one third of the number of alkoxylene groups in amolecule of the monomer. In a preferred embodiment, the alkoxylenegroups in a trifunctional alkoxylated monomer are bonded consecutivelyin three groups, where the three groups are separated by chemicallinkages and each group includes a third or approximately a third of thenumber of alkoxylene groups in the molecule.

Representative multifunctional ethylenically unsaturated monomers forthe curable secondary coating composition include, without limitation,alkoxylated bisphenol-A diacrylates, such as ethoxylated bisphenol-Adiacrylate, and alkoxylated trimethylolpropane triacrylates, such asethoxylated trimethylolpropane triacrylate, with the degree ofalkoxylation being 2 or greater, or 4 or greater, or 6 or greater, orless than 16 or less than 12, or less than 8, or less than 5, or in therange from 2 to 16, or in the range from 2 to 12, or in the range from 2to 8, or in the range from 2 to 4, or in the range from 3 to 12, or inthe range from 3 to 8, or in the range from 3 to 5, or in the range from4 to 12, or in the range from 4 to 10, or in the range from 4 to 8.

Multifunctional ethylenically unsaturated monomers for the curablesecondary coating composition include, without limitation, alkoxylatedbisphenol A diacrylates, such as ethoxylated bisphenol A diacrylate,with the degree of alkoxylation being 2 or greater. The monomercomponent of the secondary coating composition may include ethoxylatedbisphenol A diacrylate with a degree of ethoxylation ranging from 2 toabout 30 (e.g. SR349, SR601, and SR602 available from Sartomer Company,Inc. West Chester, Pa. and Photomer 4025 and Photomer 4028, availablefrom IGM Resins), or propoxylated bisphenol A diacrylate with the degreeof propoxylation being 2 or greater; for example, ranging from 2 toabout 30; methylolpropane polyacrylates with and without alkoxylationsuch as ethoxylated trimethylolpropane triacrylate with the degree ofethoxylation being 3 or greater; for example, ranging from 3 to about 30(e.g., Photomer 4149, IGM Resins, and SR499, Sartomer Company, Inc.);propoxylated-trimethylolpropane triacrylate with the degree ofpropoxylation being 3 or greater; for example, ranging from 3 to 30(e.g., Photomer 4072, IGM Resins and SR492, Sartomer);ditrimethylolpropane tetraacrylate (e.g., Photomer 4355, IGM Resins);alkoxylated glyceryl triacrylates such as propoxylated glyceryltriacrylate with the degree of propoxylation being 3 or greater (e.g.,Photomer 4096, IGM Resins and SR9020, Sartomer); erythritolpolyacrylates with and without alkoxylation, such as pentaerythritoltetraacrylate (e.g., SR295, available from Sartomer Company, Inc. (WestChester, Pa.)), ethoxylated pentaerythritol tetraacrylate (e.g., SR494,Sartomer Company, Inc.), and dipentaerythritol pentaacrylate (e.g.,Photomer 4399, IGM Resins, and SR399, Sartomer Company, Inc.);isocyanurate polyacrylates formed by reacting an appropriate functionalisocyanurate with an acrylic acid or acryloyl chloride, such astris-(2-hydroxyethyl) isocyanurate triacrylate (e.g., SR368, SartomerCompany, Inc.) and tris-(2-hydroxyethyl) isocyanurate diacrylate;alcohol polyacrylates with and without alkoxylation such astricyclodecane dimethanol diacrylate (e.g., CD406, Sartomer Company,Inc.) and ethoxylated polyethylene glycol diacrylate with the degree ofethoxylation being 2 or greater; for example, ranging from about 2 to30; epoxy acrylates formed by adding acrylate to bisphenol Adiglycidylether and the like (e.g., Photomer 3016, IGM Resins); andsingle and multi-ring cyclic aromatic or non-aromatic polyacrylates suchas dicyclopentadiene diacrylate and dicyclopentane diacrylate.

Multifunctional ethylenically unsaturated monomers of the curablesecondary coating composition include ethoxylated bisphenol-A diacrylatewith a degree of ethoxylation ranging from 2 to 16 (e.g. SR349, SR601,and SR602 available from Sartomer Company, Inc. West Chester, Pa. andPhotomer 4028, available from IGM Resins), or propoxylated bisphenol-Adiacrylate with the degree of propoxylation being 2 or greater; forexample, ranging from 2 to 16; methylolpropane polyacrylates with andwithout alkoxylation such as alkoxylated trimethylolpropane triacrylateor ethoxylated trimethylolpropane triacrylate with the degree ofalkoxylation or ethoxylation being 2 or greater; for example, rangingfrom 2 to 16 or from 3 to 10 (e.g., Photomer 4149, IGM Resins, andSR499, Sartomer Company, Inc.); propoxylated-trimethylolpropanetriacrylate with the degree of propoxylation being 2 or greater; forexample, ranging from 2 to 16 (e.g., Photomer 4072, IGM Resins andSR492, Sartomer); ditrimethylolpropane tetraacrylate (e.g., Photomer4355, IGM Resins); alkoxylated glyceryl triacrylates such aspropoxylated glyceryl triacrylate with the degree of propoxylation being2 or greater; for example, ranging from 2 to 16 (e.g., Photomer 4096,IGM Resins and SR9020, Sartomer); erythritol polyacrylates with andwithout alkoxylation, such as pentaerythritol tetraacrylate (e.g.,SR295, available from Sartomer Company, Inc. (West Chester, Pa.)),ethoxylated pentaerythritol tetraacrylate (e.g., SR494, SartomerCompany, Inc.), and dipentaerythritol pentaacrylate (e.g., Photomer4399, IGM Resins, and SR399, Sartomer Company, Inc.); isocyanuratepolyacrylates formed by reacting an appropriate functional isocyanuratewith an acrylic acid or acryloyl chloride, such as tris-(2-hydroxyethyl)isocyanurate triacrylate (e.g., SR368, Sartomer Company, Inc.) andtris-(2-hydroxyethyl) isocyanurate diacrylate; alcohol polyacrylateswith and without alkoxylation such as tricyclodecane dimethanoldiacrylate (e.g., CD406, Sartomer Company, Inc.) and ethoxylatedpolyethylene glycol diacrylate with the degree of ethoxylation being 2or greater; for example, ranging from 2 to 16; epoxy acrylates formed byadding acrylate to bisphenol-A diglycidylether and the like (e.g.,Photomer 3016, IGM Resins); and single and multi-ring cyclic aromatic ornon-aromatic polyacrylates such as dicyclopentadiene diacrylate anddicyclopentane diacrylate.

In some embodiments, the curable secondary coating composition includesa multifunctional monomer with three or more curable functional groupsin an amount greater than 2.0 wt %, or greater than 5.0 wt %, or greaterthan 7.5 wt %, or greater than 10 wt %, or greater than 15 wt %, orgreater than 20 wt %, or in the range from 2.0 wt % to 25 wt %, or inthe range from 5.0 wt % to 20 wt %, or in the range from 8.0 wt % to 15wt %. In a preferred embodiment, each of the three or more curablefunctional groups is an acrylate group.

In some embodiments, the curable secondary coating composition includesa trifunctional monomer in an amount greater than 2.0 wt %, or greaterthan 5.0 wt %, or greater than 7.5 wt %, or greater than 10 wt %, orgreater than 15 wt %, or greater than 20 wt %, or in the range from 2.0wt % to 25 wt %, or in the range from 5.0 wt % to 20 wt %, or in therange from 8.0 wt % to 15 wt %. In a preferred embodiment, thetrifunctional monomer is a triacrylate monomer.

In some embodiments, the curable secondary coating composition includesa difunctional monomer in an amount greater than 55 wt %, or greaterthan 60 wt %, or greater than 65 wt %, or greater than 70 wt %, or inthe range from 55 wt % to 80 wt %, or in the range from 60 wt % to 75 wt%, and further includes a trifunctional monomer in an amount in therange from 2.0 wt % to 25 wt %, or in the range from 5.0 wt % to 20 wt%, or in the range from 8.0 wt % to 15 wt %. In a preferred embodiment,the difunctional monomer is a diacrylate monomer and the trifunctionalmonomer is a triacrylate monomer. Preferred diacrylate monomers includealkoxylated bisphenol-A diacrylates. Preferred triacrylate monomersinclude alkoxylated trimethylolpropane triacrylates and isocyanuratetriacrylates. Preferably the curable secondary coating composition lacksan alkoxylated bisphenol-A diacrylate having a degree of alkoxylationgreater than 17, or greater than 20, or greater than 25, or in the rangefrom 15 to 40, or in the range from 20 to 35.

In some embodiments, the curable secondary coating composition lacks amonofunctional monomer and includes a difunctional monomer in an amountgreater than 55 wt %, or greater than 60 wt %, or greater than 65 wt %,or greater than 70 wt %, or in the range from 55 wt % to 80 wt %, or inthe range from 60 wt % to 75 wt %, and further includes a trifunctionalmonomer in an amount in the range from 2.0 wt % to 25 wt %, or in therange from 5.0 wt % to 20 wt %, or in the range from 8.0 wt % to 15 wt%. In a preferred embodiment, the difunctional monomer is a diacrylatemonomer and the trifunctional monomer is a triacrylate monomer.Preferred diacrylate monomers include alkoxylated bisphenol-Adiacrylates. Preferred triacrylate monomers include alkoxylatedtrimethylolpropane triacrylates and isocyanurate triacrylates.Preferably the curable secondary coating composition lacks analkoxylated bisphenol-A diacrylate having a degree of alkoxylationgreater than 17, or greater than 20, or greater than 25, or in the rangefrom 15 to 40, or in the range from 20 to 35.

In some embodiments, the curable secondary coating composition includestwo or more difunctional monomers in a combined amount greater than 70wt %, or greater than 75 wt %, or greater than 80 wt %, or greater than85 wt %, or in the range from 70 wt % to 95 wt %, or in the range from75 wt % to 90 wt %, and further includes a trifunctional monomer in anamount in the range from 2.0 wt % to 25 wt %, or in the range from 5.0wt % to 20 wt %, or in the range from 8.0 wt % to 15 wt %. In apreferred embodiment, the difunctional monomer is a diacrylate monomerand the trifunctional monomer is a triacrylate monomer. Preferreddiacrylate monomers include alkoxylated bisphenol-A diacrylates.Preferred triacrylate monomers include alkoxylated trimethylolpropanetriacrylates and isocyanurate triacrylates. Preferably the curablesecondary coating composition lacks an alkoxylated bisphenol-Adiacrylate having a degree of alkoxylation greater than 17, or greaterthan 20, or greater than 25, or in the range from 15 to 40, or in therange from 20 to 35.

In some embodiments, the curable secondary coating composition lacks amonofunctional monomer and includes two or more difunctional monomers ina combined amount greater than 70 wt %, or greater than 75 wt %, orgreater than 80 wt %, or greater than 85 wt %, or in the range from 70wt % to 95 wt %, or in the range from 75 wt % to 90 wt %, and furtherincludes a trifunctional monomer in an amount in the range from 2.0 wt %to 25 wt %, or in the range from 5.0 wt % to 20 wt %, or in the rangefrom 8.0 wt % to 15 wt %. In a preferred embodiment, the difunctionalmonomer is a diacrylate monomer and the trifunctional monomer is atriacrylate monomer. Preferred diacrylate monomers include alkoxylatedbisphenol-A diacrylates. Preferred triacrylate monomers includealkoxylated trimethylolpropane triacrylates and isocyanuratetriacrylates. Preferably the curable secondary coating composition lacksan alkoxylated bisphenol-A diacrylate having a degree of alkoxylationgreater than 17, or greater than 20, or greater than 25, or in the rangefrom 15 to 40, or in the range from 20 to 35.

In some embodiments, the curable secondary coating composition includestwo or more difunctional monomers in a combined amount greater than 70wt %, or greater than 75 wt %, or greater than 80 wt %, or greater than85 wt %, or in the range from 70 wt % to 95 wt %, or in the range from75 wt % to 90 wt %, and further includes two or more trifunctionalmonomers in a combined amount in the range from 2.0 wt % to 25 wt %, orin the range from 5.0 wt % to 20 wt %, or in the range from 8.0 wt % to15 wt %. In a preferred embodiment, each of the two or more difunctionalmonomers is a diacrylate monomer and each of the two or moretrifunctional monomers is a triacrylate monomer. Preferred diacrylatemonomers include alkoxylated bisphenol-A diacrylates. Preferredtriacrylate monomers include alkoxylated trimethylolpropane triacrylatesand isocyanurate triacrylates. Preferably the curable secondary coatingcomposition lacks an alkoxylated bisphenol-A diacrylate having a degreeof alkoxylation greater than 17, or greater than 20, or greater than 25,or in the range from 15 to 40, or in the range from 20 to 35.

In some embodiments, the curable secondary coating composition lacks amonofunctional monomer and includes two or more difunctional monomers ina combined amount greater than 70 wt %, or greater than 75 wt %, orgreater than 80 wt %, or greater than 85 wt %, or in the range from 70wt % to 95 wt %, or in the range from 75 wt % to 90 wt %, and furtherincludes two or more trifunctional monomers in a combined amount in therange from 2.0 wt % to 25 wt %, or in the range from 5.0 wt % to 20 wt%, or in the range from 8.0 wt % to 15 wt %. In a preferred embodiment,the each of the difunctional monomers is a diacrylate monomer and eachof the trifunctional monomers is a triacrylate monomer. Preferreddiacrylate monomers include alkoxylated bisphenol-A diacrylates.Preferred triacrylate monomers include alkoxylated trimethylolpropanetriacrylates and isocyanurate triacrylates. Preferably the curablesecondary coating composition lacks an alkoxylated bisphenol-Adiacrylate having a degree of alkoxylation greater than 17, or greaterthan 20, or greater than 25, or in the range from 15 to 40, or in therange from 20 to 35.

A preferred difunctional monomer is an alkoxylated bisphenol-Adiacrylate. Alkoxylated bisphenol-A diacrylate has the general formula(XIII):

where R₁ and R₂ are alkylene groups, R₁—O and R₂—O are alkoxylenegroups, and R₃ is H. Any two of the groups R₁, R₂, and R₃ are the sameor different. In one embodiment, the groups R₁ and R₂ are the same. Thenumber of carbons in each of the groups R₁ and R₂ is in the range from 1to 8, or in the range from 2 to 6, or in the range from 2 to 4. Thedegree of alkoxylation is ½(x+y). The values of x and y are the same ordifferent. In one embodiment, x and y are the same.

A preferred trifunctional monomer is an alkoxylated trimethylolpropanetriacrylate. Alkoxylated trimethylolpropane triacrylate has the generalformula (XIV):

where where R₁ and R₂ are alkylene groups, O—R₁, O—R₂, and O—R₃ arealkoxylene groups. Any two of the groups R₁, R₂, and R₃ are the same ordifferent. In one embodiment, the groups R₁, R₂, and R₃ are the same.The number of carbons in the each of the groups R₁, R₂, and R₃ is in therange from 1 to 8, or in the range from 2 to 6, or in the range from 2to 4. The degree of alkoxylation is ⅓(x+y+z). The values of any two ofx, y and z are the same or different. In one embodiment, x, y, and z arethe same.

Another preferred trifunctional monomer is a tris[(acryloyloxy)alkyl]isocyanurate. Tris[(acryloyloxy)alkyl] isocyanurates are also referredto as tris[n-hydroxyalkyl) isocyanurate triacrylates. A representativetris[(acryloyloxy)alkyl] isocyanurate is tris[2-hydroxyethyl)isocyanurate triacrylate, which has the general formula (XV):

In formula (III), an ethylene linkage (—CH₂—CH₂—) bonds each acryloyloxygroup to a nitrogen of the isocyanurate ring. In other embodiments oftris[(acryloyloxy)alkyl] isocyanurates, alkylene linkages other thanethylene bond the acryloyloxy groups to nitrogen atoms of theisocyanurate ring. The alkylene linkages for any two of the threealkylene linkages are the same or different. In one embodiment, thethree alkylene linkages are the same. The number of carbons in each ofthe alkylene linkages is in the range from 1 to 8, or in the range from2 to 6, or in the range from 2 to 4.

In one embodiment, the curable secondary composition includes analkoxylated bisphenol-A diacrylate monomer in an amount greater than 55wt %, or greater than 60 wt %, or greater than 65 wt %, or greater than70 wt %, or in the range from 55 wt % to 80 wt %, or in the range from60 wt % to 75 wt %, and further includes an alkoxylatedtrimethylolpropane triacrylate monomer in an amount in the range from2.0 wt % to 25 wt %, or in the range from 5.0 wt % to 20 wt %, or in therange from 8.0 wt % to 15 wt %. Preferably the curable secondary coatingcomposition lacks an alkoxylated bisphenol-A diacrylate having a degreeof alkoxylation greater than 17, or greater than 20, or greater than 25,or in the range from 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includes analkoxylated bisphenol-A diacrylate monomer in an amount greater than 55wt %, or greater than 60 wt %, or greater than 65 wt %, or greater than70 wt %, or in the range from 55 wt % to 80 wt %, or in the range from60 wt % to 75 wt %, and further includes an ethoxylatedtrimethylolpropane triacrylate monomer in an amount in the range from2.0 wt % to 25 wt %, or in the range from 5.0 wt % to 20 wt %, or in therange from 8.0 wt % to 15 wt %. Preferably the curable secondary coatingcomposition lacks an alkoxylated bisphenol-A diacrylate having a degreeof alkoxylation greater than 17, or greater than 20, or greater than 25,or in the range from 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includes anethoxylated bisphenol-A diacrylate monomer in an amount greater than 55wt %, or greater than 60 wt %, or greater than 65 wt %, or greater than70 wt %, or in the range from 55 wt % to 80 wt %, or in the range from60 wt % to 75 wt %, and further includes an alkoxylatedtrimethylolpropane triacrylate monomer in an amount in the range from2.0 wt % to 25 wt %, or in the range from 5.0 wt % to 20 wt %, or in therange from 8.0 wt % to 15 wt %. Preferably the curable secondary coatingcomposition lacks an alkoxylated bisphenol-A diacrylate having a degreeof alkoxylation greater than 17, or greater than 20, or greater than 25,or in the range from 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includes anethoxylated bisphenol-A diacrylate monomer in an amount greater than 55wt %, or greater than 60 wt %, or greater than 65 wt %, or greater than70 wt %, or in the range from 55 wt % to 80 wt %, or in the range from60 wt % to 75 wt %, and further includes an ethoxylatedtrimethylolpropane triacrylate monomer in an amount in the range from2.0 wt % to 25 wt %, or in the range from 5.0 wt % to 20 wt %, or in therange from 8.0 wt % to 15 wt %. Preferably the curable secondary coatingcomposition lacks an alkoxylated bisphenol-A diacrylate having a degreeof alkoxylation greater than 17, or greater than 20, or greater than 25,or in the range from 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includes analkoxylated bisphenol-A diacrylate monomer in an amount greater than 55wt %, or greater than 60 wt %, or greater than 65 wt %, or greater than70 wt %, or in the range from 55 wt % to 80 wt %, or in the range from60 wt % to 75 wt %, and further includes a tris[(acryloyloxy)alkyl]isocyanurate monomer in an amount in the range from 2.0 wt % to 25 wt %,or in the range from 5.0 wt % to 20 wt %, or in the range from 8.0 wt %to 15 wt %. Preferably the curable secondary coating composition lacksan alkoxylated bisphenol-A diacrylate having a degree of alkoxylationgreater than 17, or greater than 20, or greater than 25, or in the rangefrom 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includes anethoxylated bisphenol-A diacrylate monomer in an amount greater than 55wt %, or greater than 60 wt %, or greater than 65 wt %, or greater than70 wt %, or in the range from 55 wt % to 80 wt %, or in the range from60 wt % to 75 wt %, and further includes a tris[(acryloyloxy)alkyl]isocyanurate monomer in an amount in the range from 2.0 wt % to 25 wt %,or in the range from 5.0 wt % to 20 wt %, or in the range from 8.0 wt %to 15 wt %. Preferably the curable secondary coating composition lacksan alkoxylated bisphenol-A diacrylate having a degree of alkoxylationgreater than 17, or greater than 20, or greater than 25, or in the rangefrom 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includes analkoxylated bisphenol-A diacrylate monomer in an amount greater than 55wt %, or greater than 60 wt %, or greater than 65 wt %, or greater than70 wt %, or in the range from 55 wt % to 80 wt %, or in the range from60 wt % to 75 wt %, and further includes tris(2-hydroxyethyl)isocyanurate triacrylate monomer in an amount in the range from 2.0 wt %to 25 wt %, or in the range from 5.0 wt % to 20 wt %, or in the rangefrom 8.0 wt % to 15 wt %. Preferably the curable secondary coatingcomposition lacks an alkoxylated bisphenol-A diacrylate having a degreeof alkoxylation greater than 17, or greater than 20, or greater than 25,or in the range from 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includes anethoxylated bisphenol-A diacrylate monomer in an amount greater than 55wt %, or greater than 60 wt %, or greater than 65 wt %, or greater than70 wt %, or in the range from 55 wt % to 80 wt %, or in the range from60 wt % to 75 wt %, and further includes a tris(2-hydroxyethyl)isocyanurate triacrylate monomer in an amount in the range from 2.0 wt %to 25 wt %, or in the range from 5.0 wt % to 20 wt %, or in the rangefrom 8.0 wt % to 15 wt %. Preferably the curable secondary coatingcomposition lacks an alkoxylated bisphenol-A diacrylate having a degreeof alkoxylation greater than 17, or greater than 20, or greater than 25,or in the range from 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includesbisphenol-A epoxy diacrylate monomer in an amount greater than 5.0 wt %,or greater than 10 wt %, or greater than 15 wt %, or in the range from5.0 wt % to 20 wt % or in the range from 8 wt % to 17 wt %, or in therange from 10 wt % to 15 wt %, and further includes an alkoxylatedbisphenol-A diacrylate monomer in an amount greater than 55 wt %, orgreater than 60 wt %, or greater than 65 wt %, or greater than 70 wt %,or in the range from 55 wt % to 80 wt %, or in the range from 60 wt % to75 wt %, and further includes an alkoxylated trimethylolpropanetriacrylate monomer in an amount in the range from 2.0 wt % to 25 wt %,or in the range from 5.0 wt % to 20 wt %, or in the range from 8.0 wt %to 15 wt %. Preferably the curable secondary coating composition lacksan alkoxylated bisphenol-A diacrylate having a degree of alkoxylationgreater than 17, or greater than 20, or greater than 25, or in the rangefrom 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includesbisphenol-A epoxy diacrylate monomer in an amount greater than 5.0 wt %,or greater than 10 wt %, or greater than 15 wt %, or in the range from5.0 wt % to 20 wt % or in the range from 8 wt % to 17 wt %, or in therange from 10 wt % to 15 wt %, and further includes an alkoxylatedbisphenol-A diacrylate monomer in an amount greater than 55 wt %, orgreater than 60 wt %, or greater than 65 wt %, or greater than 70 wt %,or in the range from 55 wt % to 80 wt %, or in the range from 60 wt % to75 wt %, and further includes an ethoxylated trimethylolpropanetriacrylate monomer in an amount in the range from 2.0 wt % to 25 wt %,or in the range from 5.0 wt % to 20 wt %, or in the range from 8.0 wt %to 15 wt %. Preferably the curable secondary coating composition lacksan alkoxylated bisphenol-A diacrylate having a degree of alkoxylationgreater than 17, or greater than 20, or greater than 25, or in the rangefrom 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includesbisphenol-A epoxy diacrylate monomer in an amount greater than 5.0 wt %,or greater than 10 wt %, or greater than 15 wt %, or in the range from5.0 wt % to 20 wt % or in the range from 8 wt % to 17 wt %, or in therange from 10 wt % to 15 wt %, and further includes an ethoxylatedbisphenol-A diacrylate monomer in an amount greater than 55 wt %, orgreater than 60 wt %, or greater than 65 wt %, or greater than 70 wt %,or in the range from 55 wt % to 80 wt %, or in the range from 60 wt % to75 wt %, and further includes an alkoxylated trimethylolpropanetriacrylate monomer in an amount in the range from 2.0 wt % to 25 wt %,or in the range from 5.0 wt % to 20 wt %, or in the range from 8.0 wt %to 15 wt %. Preferably the curable secondary coating composition lacksan alkoxylated bisphenol-A diacrylate having a degree of alkoxylationgreater than 17, or greater than 20, or greater than 25, or in the rangefrom 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includesbisphenol-A epoxy diacrylate monomer in an amount greater than 5.0 wt %,or greater than 10 wt %, or greater than 15 wt %, or in the range from5.0 wt % to 20 wt % or in the range from 8 wt % to 17 wt %, or in therange from 10 wt % to 15 wt %, and further includes an ethoxylatedbisphenol-A diacrylate monomer in an amount greater than 55 wt %, orgreater than 60 wt %, or greater than 65 wt %, or greater than 70 wt %,or in the range from 55 wt % to 80 wt %, or in the range from 60 wt % to75 wt %, and further includes an ethoxylated trimethylolpropanetriacrylate monomer in an amount in the range from 2.0 wt % to 25 wt %,or in the range from 5.0 wt % to 20 wt %, or in the range from 8.0 wt %to 15 wt %. Preferably the curable secondary coating composition lacksan alkoxylated bisphenol-A diacrylate having a degree of alkoxylationgreater than 17, or greater than 20, or greater than 25, or in the rangefrom 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includesbisphenol-A epoxy diacrylate monomer in an amount greater than 5.0 wt %,or greater than 10 wt %, or greater than 15 wt %, or in the range from5.0 wt % to 20 wt % or in the range from 8 wt % to 17 wt %, or in therange from 10 wt % to 15 wt %, and further includes an alkoxylatedbisphenol-A diacrylate monomer in an amount greater than 55 wt %, orgreater than 60 wt %, or greater than 65 wt %, or greater than 70 wt %,or in the range from 55 wt % to 80 wt %, or in the range from 60 wt % to75 wt %, and further includes a tris[(acryloyloxy)alkyl] isocyanuratemonomer in an amount in the range from 2.0 wt % to 25 wt %, or in therange from 5.0 wt % to 20 wt %, or in the range from 8.0 wt % to 15 wt%. Preferably the curable secondary coating composition lacks analkoxylated bisphenol-A diacrylate having a degree of alkoxylationgreater than 17, or greater than 20, or greater than 25, or in the rangefrom 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includesbisphenol-A epoxy diacrylate monomer in an amount greater than 5.0 wt %,or greater than 10 wt %, or greater than 15 wt %, or in the range from5.0 wt % to 20 wt % or in the range from 8 wt % to 17 wt %, or in therange from 10 wt % to 15 wt %, and further includes an ethoxylatedbisphenol-A diacrylate monomer in an amount greater than 55 wt %, orgreater than 60 wt %, or greater than 65 wt %, or greater than 70 wt %,or in the range from 55 wt % to 80 wt %, or in the range from 60 wt % to75 wt %, and further includes a tris[(acryloyloxy)alkyl] isocyanuratemonomer in an amount in the range from 2.0 wt % to 25 wt %, or in therange from 5.0 wt % to 20 wt %, or in the range from 8.0 wt % to 15 wt%. Preferably the curable secondary coating composition lacks analkoxylated bisphenol-A diacrylate having a degree of alkoxylationgreater than 17, or greater than 20, or greater than 25, or in the rangefrom 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includesbisphenol-A epoxy diacrylate monomer in an amount greater than 5.0 wt %,or greater than 10 wt %, or greater than 15 wt %, or in the range from5.0 wt % to 20 wt % or in the range from 8 wt % to 17 wt %, or in therange from 10 wt % to 15 wt %, and further includes an alkoxylatedbisphenol-A diacrylate monomer in an amount greater than 55 wt %, orgreater than 60 wt %, or greater than 65 wt %, or greater than 70 wt %,or in the range from 55 wt % to 80 wt %, or in the range from 60 wt % to75 wt %, and further includes tris(2-hydroxyethyl) isocyanuratetriacrylate monomer in an amount in the range from 2.0 wt % to 25 wt %,or in the range from 5.0 wt % to 20 wt %, or in the range from 8.0 wt %to 15 wt %. Preferably the curable secondary coating composition lacksan alkoxylated bisphenol-A diacrylate having a degree of alkoxylationgreater than 17, or greater than 20, or greater than 25, or in the rangefrom 15 to 40, or in the range from 20 to 35.

In one embodiment, the curable secondary composition includesbisphenol-A epoxy diacrylate monomer in an amount greater than 5.0 wt %,or greater than 10 wt %, or greater than 15 wt %, or in the range from5.0 wt % to 20 wt % or in the range from 8 wt % to 17 wt %, or in therange from 10 wt % to 15 wt %, and further includes an ethoxylatedbisphenol-A diacrylate monomer in an amount greater than 55 wt %, orgreater than 60 wt %, or greater than 65 wt %, or greater than 70 wt %,or in the range from 55 wt % to 80 wt %, or in the range from 60 wt % to75 wt %, and further includes a tris(2-hydroxyethyl) isocyanuratetriacrylate monomer in an amount in the range from 2.0 wt % to 25 wt %,or in the range from 5.0 wt % to 20 wt %, or in the range from 8.0 wt %to 15 wt %. Preferably the curable secondary coating composition lacksan alkoxylated bisphenol-A diacrylate having a degree of alkoxylationgreater than 17, or greater than 20, or greater than 25, or in the rangefrom 15 to 40, or in the range from 20 to 35.

The optional oligomer present in the radiation-curable secondary coatingcomposition is preferably a compound with urethane linkages. In oneaspect, the optional oligomer is a reaction product of a polyolcompound, a diisocyanate compound, and a hydroxy-functional acrylatecompound. Reaction of the polyol compound with the diisocyanate compoundprovides a urethane linkage and the hydroxy-functional acrylate compoundreacts with isocyanate groups to provide terminal acrylate groups. Ifpresent, the total oligomer content in the radiation-curable secondarycoating composition is less than 3.0 wt %, or less than 2.0 wt %, orless than 1.0 wt %, or in the range from 0 wt % to 3.0 wt %, or in therange from 0.1 wt % to 3.0 wt %, or in the range from 0.2 wt % to 2.0 wt%, or in the range from 0.3 wt % to 1.0 wt %. In one embodiment, theradiation-curable secondary coating composition is devoid of oligomers.

One class of optional oligomers is ethylenically unsaturated oligomers.When included, suitable oligomers may be monofunctional oligomers,multifunctional oligomers, or a combination of a monofunctional oligomerand a multifunctional oligomer. If present, the oligomer component mayinclude aliphatic and aromatic urethane (meth)acrylate oligomers, urea(meth)acrylate oligomers, polyester and polyether (meth)acrylateoligomers, acrylated acrylic oligomers, polybutadiene (meth)acrylateoligomers, polycarbonate (meth)acrylate oligomers, and melamine(meth)acrylate oligomers or combinations thereof. The curable secondarycoating composition may be free of urethane groups, urethane acrylatecompounds, urethane oligomers, or urethane acrylate oligomers.

The optional oligomeric component of the curable secondary coatingcomposition may include a difunctional oligomer. A difunctional oligomerhas a structure according to formula (XVI) below:

F₁—R₈-[urethane-R₉-urethane]_(m)-R₈—F₁  (XVI)

where F₁ may independently be a reactive functional group such asacrylate, methacrylate, acrylamide, N-vinyl amide, styrene, vinyl ether,vinyl ester, or other functional group known in the art; R₈ may include,independently, —(CH₂)₂₋₁₂—O—, —((CH₂)₂₋₄—O)_(n)—,—(CH₂)₂₋₁₂O—((CH₂)₂₋₄—O)_(n)—, —(CH₂)₂₋₁₂—O—(CO—(CH₂)₂₋₅—O)_(n)—, or—(CH₂)₂₋₁₂—O(CO(CH₂)₂₋₅—NH)_(n)— where n is a whole number from 1 to 30,including, for example, from 1 to 10; R₉ may be a polyether, polyester,polycarbonate, polyamide, polyurethane, polyurea, or combinationthereof; and m is a whole number from 1 to 10, including, for example,from 1 to 5. In the structure of formula (I), the urethane moiety may bethe residue formed from the reaction of a diisocyanate with R₉ and/orR₈. The term “independently” is used herein to indicate that each F maydiffer from another F₁ and the same is true for each R₈.

The optional oligomer component of the curable coating composition mayinclude a multifunctional oligomer. The multifunctional oligomer mayhave a structure according to formula (XVII), formula (XVIIII), orformula (XIX) set forth below:

multiurethane-(F₂—R₈—F₂)_(x)  (XVII)

polyol-[(urethane-R₉-urethane)_(m)-R₈—F₂]_(x)  (XVIII)

multiurethane-(R₈—F₂)_(x)  (XIX)

where F₂ may independently represent from 1 to 3 functional groups suchas acrylate, methacrylate, acrylamide, N-vinyl amide, styrene, vinylether, vinyl ester, or other functional groups known in the art; R₈ caninclude —(CH₂)₂₋₁₂—O—, —((CH₂)₂₋₄—O)_(n)—,—(CH₂)₂₋₁₂O—((CH₂)₂₋₄—O)_(n)—, —(CH₂)₂₋₁₂—O—(CO—(CH₂)₂₋₅—O)_(n)—, or—(CH₂)₂₋₁₂—O—(CO—(CH₂)₂₋₅—NH)_(n)— where n is a whole number from 1 to10, including, for example, from 1 to 5; R₉ may be polyether, polyester,polycarbonate, polyamide, polyurethane, polyurea or combinationsthereof; x is a whole number from 1 to 10, including, for example, from2 to 5; and m is a whole number from 1 to 10, including, for example,from 1 to 5. In the structure of formula (XVII) of (XIX), themultiurethane group may be the residue formed from reaction of amultiisocyanate with R₉. Similarly, the urethane group in the structureof formula (XVIII) may be the reaction product formed following bondingof a diisocyanate to R₉ and/or R₈.

Urethane oligomers may be prepared by reacting an aliphatic or aromaticdiisocyanate with a dihydric polyether or polyester, most typically apolyoxyalkylene glycol such as a polyethylene glycol. Moisture-resistantoligomers may be synthesized in an analogous manner, except that polarpolyethers or polyester glycols are avoided in favor of predominantlysaturated and predominantly nonpolar aliphatic diols. These diols mayinclude alkane or alkylene diols of from about 2-250 carbon atoms thatmay be substantially free of ether or ester groups.

Polyurea elements may be incorporated in oligomers prepared by thesemethods, for example, by substituting diamines or polyamines for diolsor polyols in the course of synthesis.

The curable secondary coating composition also includes a photoinitiatorand optionally includes additives such as anti-oxidant(s), opticalbrightener(s), amine synergist(s), tackifier(s), catalyst(s), a carrieror surfactant, and a stabilizer as described above in connection withthe curable primary coating composition.

The curable secondary coating composition includes a singlephotoinitiator or a combination of two or more photoinitiators. Thetotal photoinitiator content of the curable secondary coatingcomposition is up to about 10 wt %, or between about 0.5 wt % and about6 wt %.

A representative antioxidant is thiodiethylenebis[3-(3,5-di-tert-butyl)-4-hydroxy-phenyl) propionate] (e.g., IRGANOX1035, available from BASF). In some aspects, an antioxidant is presentin the curable secondary coating composition in an amount greater than0.25 wt %, or greater than 0.50 wt %, or greater than 0.75 wt %, orgreater than 1.0 wt %, or an amount in the range from 0.25 wt % to 3.0wt %, or an amount in the range from 0.50 wt % to 2.0 wt %, or an amountin the range from 0.75 wt % to 1.5 wt %.

Representative optical brighteners include TINOPAL OB (available fromBASF); Blankophor KLA (available from Bayer); bisbenzoxazole compounds;phenylcoumarin compounds; and bis(styryl)biphenyl compounds. In anembodiment, the optical brightener is present in the curable secondarycoating composition at a concentration of 0.005 wt % to 0.3 wt %.

Representative amine synergists include triethanolamine;1,4-diazabicyclo[2.2.2]octane (DABCO), triethylamine, andmethyldiethanolamine. In an embodiment, an amine synergist is present ata concentration of 0.02 wt % to 0.5 wt %.

Secondary Coating—Properties. Relevant properties of the secondarycoating include radius, thickness, Young's modulus, tensile strength,yield strength, elongation at yield, and puncture resistance

The radius r₆ of the secondary coating is less than or equal to 100.0μm, or less than or equal to 95.0 μm, or less than or equal to 90.0 μm,or less than or equal to 85.0 μm, or less than or equal to 80.0 μm, orin the range from 77.5 μm to 100.0 μm, or in the range from 77.5 μm to97.5 μm, or in the range from 77.5 μm to 95.0 μm, or in the range from77.5 μm to 92.5 μm, or in the range from 77.5 μm to 90.0 μm, or in therange from 80.0 μm to 100.0 μm, or in the range from 80.0 μm to 97.5 μm,or in the range from 80.0 μm to 95.0 μm, or in the range from 80.0 μm to92.5 μm, or in the range from 80.0 μm to 90.0 μm, or in the range from82.5 μm to 100.0 μm, or in the range from 82.5 μm to 97.5 μm, or in therange from 82.5 μm to 95.0 μm, or in the range from 82.5 μm to 92.5 μm,or in the range from 82.5 μm to 90.0 μm.

To facilitate decreases in the diameter of the optical fiber, it ispreferable to minimize the thickness r₆−r₅ of the secondary coating. Thethickness r₆−r₅ of the secondary coating is in the range from 15.0 μm to32.5 μm, or in the range from 17.5 μm to 32.5 μm, or in the range from20.0 μm to 32.5 μm, or in the range from 22.5 μm to 32.5 μm, or in therange from 25.0 μm to 32.5 μm, or in the range from 27.5 μm to 32.5 μm,or in the range from 15.0 μm to 30.0 μm, or in the range from 17.5 μm to30.0 μm, or in the range from 20.0 μm to 30.0 μm, or in the range from22.5 μm to 30.0 μm, or in the range from 25.0 μm to 30.0 μm, or in therange from 15.0 μm to 27.5 μm, or in the range from 17.5 μm to 27.5 μm,or in the range from 20.0 μm to 27.5 μm, or in the range from 15.0 μm to25.0 μm.

To facilitate puncture resistance and high protective function, it ispreferable for the secondary coating to have a high Young's modulus. TheYoung's modulus of the secondary coating is greater than or equal to1600 MPa, or greater than or equal to 1800 MPa, or greater than or equalto 2000 MPa, or greater than or equal to 2200 MPa, or in the range from1600 MPa to 2800 MPa, or in the range from 1800 MPa to 2600 MPa.

Fiber Draw Process. In a continuous optical fiber manufacturing process,a glass fiber is drawn from a heated preform and sized to a targetdiameter (typically 125 μm). In some embodiments, the glass fiberdiameter is 125 microns. In some other embodiments, the fiber glassdiameter is less than 110 microns. In still other embodiments, the fiberglass dimeter is less than 100 microns. The glass fiber is then cooledand directed to a coating system that applies a liquid primary coatingcomposition to the glass fiber. Two process options are viable afterapplication of the liquid primary coating composition to the glassfiber. In one process option (wet-on-dry process), the liquid primarycoating composition is cured to form a solidified primary coating, theliquid secondary coating composition is applied to the cured primarycoating, and the liquid secondary coating composition is cured to form asolidified secondary coating. In a second process option (wet-on-wetprocess), the liquid secondary coating composition is applied to theliquid primary coating composition, and both liquid coating compositionsare cured simultaneously to provide solidified primary and secondarycoatings. After the fiber exits the coating system, the fiber iscollected and stored at room temperature. Collection of the fibertypically entails winding the fiber on a spool and storing the spool.

In some processes, the coating system further applies a tertiary coatingcomposition to the secondary coating and cures the tertiary coatingcomposition to form a solidified tertiary coating. Typically, thetertiary coating is an ink layer used to mark the fiber foridentification purposes and has a composition that includes a pigmentand is otherwise similar to the secondary coating. The tertiary coatingis applied to the secondary coating and cured. The secondary coating hastypically been cured at the time of application of the tertiary coating.The primary, secondary, and tertiary coating compositions can be appliedand cured in a common continuous manufacturing process. Alternatively,the primary and secondary coating compositions are applied and cured ina common continuous manufacturing process, the coated fiber iscollected, and the tertiary coating composition is applied and cured ina separate offline process to form the tertiary coating.

The wavelength of curing radiation is infrared, visible, or ultraviolet(UV). Representative wavelengths include wavelengths in the range from250 nm to 1000 nm, or in the range from 250 nm to 700 nm, or in therange from 250 nm to 450 nm, or in the range from 275 nm to 425 nm, orin the range from 300 nm to 400 nm, or in the range from 320 nm to 390nm, or in the range from 330 nm to 380 nm, or in the range from 340 nmto 370 nm. Curing can be accomplished with light sources that include alamp source (e.g. Hg lamp), an LED source (e.g. a UVLED, visible LED, orinfrared LED), or a laser source.

Each of the primary, secondary, and tertiary compositions are curablewith any of the wavelengths and any of the light sources referred toabove. The same wavelength or source can be used to cure each of theprimary, secondary, and tertiary compositions, or different wavelengthsand/or different sources can be used to cure the primary, secondary, andtertiary compositions. Curing of the primary, secondary, and tertiarycompositions can be accomplished with a single wavelength or acombination of two or more wavelengths.

To improve process efficiency, it is desirable to increase the drawspeed of the fiber along the process pathway extending from the preformto the collection point. As the draw speed increases, however, the curespeed of coating compositions must increase. The coating compositionsdisclosed herein are compatible with fiber draw processes that operateat a draw speed greater than 35 m/s, or greater than 40 m/s, or greaterthan 45 m/s, or greater than 50 m/s, or greater than 55 m/s, or greaterthan 60 m/s, or greater than 65 m/s, or greater than 70 m/s.

The present disclosure extends to optical fibers coated with the curedproduct of the coating compositions. The optical fiber includes a glasswaveguide with a higher index glass core region surrounded by a lowerindex glass cladding region. A coating formed as a cured product of thepresent coating compositions surrounds and is in direct contact with theglass cladding. The cured product of the present coating compositionsfunctions as a primary coating, secondary coating, or tertiary coatingof the fiber.

Examples—Primary Coatings

The following examples illustrate preparation of a representativeprimary coatings. Measurements of selected properties of therepresentative primary coatings are also described.

Primary Coating—Oligomer. The representative primary coatingcompositions included an oligomer. For purposes of illustration,preparation of exemplary oligomers from H12MDI (4,4′-methylenebis(cyclohexyl isocyanate), PPG4000 (polypropylene glycol withM_(n)˜4000 g/mol) and HEA (2-hydroxyethyl acrylate) in accordance withthe reaction scheme hereinabove is described. All reagents were used assupplied by the manufacturer and were not subjected to furtherpurification. H12MDI was obtained from ALDRICH. PPG4000 was obtainedfrom COVESTRO and was certified to have an unsaturation of 0.004 meq/gas determined by the method described in the standard ASTM D4671-16. HEAwas obtained from KOWA.

The relative amounts of the reactants and reaction conditions werevaried to obtain a series of six oligomers. Oligomers with differentinitial molar ratios of the constituents were prepared with molar ratiosof the reactants satisfying H12MDI:HEA:PPG4000=n:m:p, where n was in therange from 3.0 to 4.0, m was in the range from 1.5n to 3 to 2.5n to 5,and p=2. In the reactions used to form the oligomers materials,dibutyltin dilaurate was used as a catalyst (at a level of 160 ppm basedon the mass of the initial reaction mixture) and2,6-di-tert-butyl-4-methylphenol (BHT) was used as an inhibitor (at alevel of 400 ppm based on the mass of the initial reaction mixture).

The amounts of the reactants used to prepare each of the six oligomersare summarized in Table 1 below. The six oligomers are identified byseparate Sample numbers 1-6. Corresponding sample numbers will be usedherein to refer to coating compositions and cured films formed fromcoating compositions that individually contain each of the sixoligomers. The corresponding mole numbers used in the preparation ofeach of the six samples are listed in Table 2 below. The mole numbersare normalized to set the mole number p of PPG4000 to 2.0.

TABLE 1 Reactants and Amounts for Exemplary Oligomer Samples 1-6 SampleH12MDI (g) HEA (g) PPG4000 (g) 1 22  6.5 221.5 2 26.1 10.6 213.3 3 26.110.6 213.3 4 27.8 12.3 209.9 5 27.8 12.3 209.9 6 22  6.5 221.5

TABLE 2 Mole Numbers for Oligomer Samples 1-6 HEA PPG4000 H12MDI MoleMole Di-adduct Sample Mole Number (n) Number (m) Number (p) (wt %) 1 3.02.0 2.0 1.3 2 3.7 3.4 2.0 3.7 3 3.7 3.4 2.0 3.7 4 4.0 4.0 2.0 5.0 5 4.04.0 2.0 5.0 6 3.0 2.0 2.0 1.3

The oligomers were prepared by mixing 4,4′-methylene bis(cyclohexylisocyanate), dibutyltin dilaurate and 2,6-di-tert-butyl-4 methylphenolat room temperature in a 500 mL flask. The 500 mL flask was equippedwith a thermometer, a CaCl₂ drying tube, and a stirrer. Whilecontinuously stirring the contents of the flask, PPG4000 was added overa time period of 30-40 minutes using an addition funnel. The internaltemperature of the reaction mixture was monitored as the PPG4000 wasadded and the introduction of PPG4000 was controlled to prevent excessheating (arising from the exothermic nature of the reaction). After thePPG4000 was added, the reaction mixture was heated in an oil bath atabout 70° C. to 75° C. for about 1 to 1½ hours. At various intervals,samples of the reaction mixture were retrieved for analysis by infraredspectroscopy (FTIR) to monitor the progress of the reaction bydetermining the concentration of unreacted isocyanate groups. Theconcentration of unreacted isocyanate groups was assessed based on theintensity of a characteristic isocyanate stretching mode near 2265 cm⁻¹.The flask was removed from the oil bath and its contents were allowed tocool to below 65° C. Addition of supplemental HEA was conducted toinsure complete quenching of isocyanate groups. The supplemental HEA wasadded dropwise over 2-5 minutes using an addition funnel. After additionof the supplemental HEA, the flask was returned to the oil bath and itscontents were again heated to about 70° C. to 75° C. for about 1 to 1½hours. FTIR analysis was conducted on the reaction mixture to assess thepresence of isocyanate groups and the process was repeated until enoughsupplemental HEA was added to fully react any unreacted isocyanategroups. The reaction was deemed complete when no appreciable isocyanatestretching intensity was detected in the FTIR measurement. The HEAamounts listed in Table 1 include the initial amount of HEA in thecomposition and any amount of supplemental HEA needed to quenchunreacted isocyanate groups.

The concentration (wt %) of di-adduct compound in each oligomer wasdetermined by gel permeation chromatography (GPC). A Waters Alliance2690 GPC instrument was used to determine the di-adduct concentration.The mobile phase was THF. The instrument included a series of threePolymer Labs columns. Each column had a length of 300 mm and an insidediameter of 7.5 mm. Two of the columns (columns 1 and 2) were sold underPart No. PL1110-6504 by Agilent Technologies and were packed with PLgelMixed D stationary phase (polystyrene divinyl benzene copolymer, averageparticle size=5 μm, specified molecular weight range=200 g/mol to400,000 g/mol). The third column (column 3) was sold under Part No.PL1110-6520 by Agilent Technologies and was packed with PLgel 100Astationary phase (polystyrene divinyl benzene copolymer, averageparticle size=5 μm, specified molecular weight range=up to 4,000 g/mol).The columns were calibrated with polystyrene standards ranging from 162g/mol to 6,980,000 g/mol using EasiCal PS-1 & 2 polymer calibrant kits(Agilent Technologies Part Nos. PL2010-505 and PL2010-0601). The GPCinstrument was operated under the following conditions: flow rate=1.0mL/min, column temperature=40° C., injection volume=100 μL, and runtime=35 min (isocratic conditions). The detector was a Waters Alliance2410 differential refractometer operated at 40° C. and sensitivity level4. The samples were injected twice along with a THF+0.05% toluene blank.

The amount (wt %) of di-adduct in the oligomers was quantified using thepreceding GPC system and technique. A calibration curve was obtainedusing standard solutions containing known amounts of the di-adductcompound (HEA˜H12MDI˜HEA) in THF. Standard solutions with di-adductconcentrations of 115.2 μg/g, 462.6 μg/g, 825.1 μg/g, and 4180 μg/g wereprepared. (As used herein, the dimension “μg/g” refers to μg ofdi-adduct per gram of total solution (di-adduct+THF)). Two 100 μLaliquots of each di-adduct standard solution were injected into thecolumn to obtain the calibration curve. The retention time of thedi-adduct was approximately 23 min and the area of the GPC peak of thedi-adduct was measured and correlated with di-adduct concentration. Alinear correlation of peak area as a function of di-adduct concentrationwas obtained (correlation coefficient (R²)=0.999564).

The di-adduct concentration in the oligomers was determined using thecalibration. Samples were prepared by diluting ˜0.10 g of oligomericmaterial in THF to obtain a ˜1.5 g test solution. The test solution wasrun through the GPC instrument and the area of the peak associated withthe di-adduct compound was determined. The di-adduct concentration inunits of μg/g was obtained from the peak area and the calibration curve,and was converted to wt % by multiplying by the weight (g) of the testsolution and dividing by the weight of the sample of oligomeric materialbefore dilution with THF. The wt % of di-adduct compound present in eachof the six oligomers prepared in this example are reported in Table 2.

Through variation in the relative mole ratios of H12MDI, HEA, andPPG4000, the illustrative oligomers include a polyether urethanecompound of the type shown in molecular formula (IV) hereinabove and anenhanced concentration of di-adduct compound of the type shown inmolecular formula (V) hereinabove.

Primary Coating—Compositions. Oligomers corresponding to Samples 1-6were separately combined with other components to form a series of sixrepresentative primary coating compositions. The amount of eachcomponent in the coating composition is listed in Table 3 below. Theentry in Table 3 for the oligomer includes the combined amount ofpolyether urethane acrylate compound and di-adduct compound present inthe oligomer. A separate coating composition was made for each of thesix exemplary oligomers corresponding to Samples 1-6, where the amountof di-adduct compound in the oligomeric material corresponded to theamount listed in Table 2.

TABLE 3 Coating Composition Component Amount Oligomeric Material 49.10wt % Sartomer SR504 45.66 wt % V-CAP/RC  1.96 wt % TPO  1.47 wt %Irganox 1035  0.98 wt % adhesion promoter  0.79 wt % Tetrathiol  0.03 wt%

Sartomer SR504 is ethoxylated(4)nonylphenol acrylate (available fromSartomer). V-CAP/RC is N-vinylcaprolactam (available from ISPTechnologies). TPO is 2,4,6-trimethylbenzoyl)diphenyl phosphine oxide(available from BASF under the trade name Lucirin and functions as aphotoinitiator). Irganox 1035 is thiodiethylenebis[3-(3,5-di-tert-butyl)-4-hydroxy-phenyl) propionate] (available fromBASF) and functions as an antioxidant. The adhesion promoters were3-acryloxypropyl trimethoxysilane (available from Gelest) and3-mercaptopropyl trimethoxysilane (available from Aldrich).3-acryloxypropyl trimethoxysilane was used for Samples 1, 3, and 5.3-mercaptopropyl trimethoxysilane was used for Samples 2, 4, and 6.Tetrathiol is a catalyst quencher.

The coating compositions of Table 3 were each formulated using ahigh-speed mixer in an appropriate container heated to 60° C., with aheating band or heating mantle. In each case, the components wereweighed into the container using a balance and allowed to mix until thesolid components were thoroughly dissolved and the mixture appearedhomogeneous. The oligomer and monomers (SR504, NVC) of each compositionwere blended together for at least 10 minutes at 55° C. to 60° C. Thephotoinitiator, antioxidant, and catalyst quencher were then added, andblending was continued for one hour while maintaining a temperature of55° C. to 60° C. Finally, the adhesion promoter was added, and blendingwas continued for 30 minutes at 55° C. to 60° C. to form the coatingcompositions.

Primary Coating—Properties—Tensile Properties. Tensile properties(Young's modulus, tensile strength at yield, and elongation at yield)were measured on films formed by curing the six coating compositions.Separate films were formed from each coating composition. Wet films ofthe coating composition were cast on silicone release paper with the aidof a draw-down box having a gap thickness of about 0.005″. The wet filmswere cured with a UV dose of 1.2 J/cm² (measured over a wavelength rangeof 225 to 424 nm by a Light Bug model IL490 from International Light) bya Fusion Systems UV curing apparatus with a 600 W/in D-bulb (50% Powerand approximately 12 ft/min belt speed) to yield cured coatings in filmform. Cured film thickness was between about 0.0030″ and 0.0035″.

The films were aged (23° C., 50% relative humidity) for at least 16hours prior to testing. Film samples were cut to dimensions of 12.5cm×13 mm using a cutting template and a scalpel. Young's modulus,tensile strength at yield, and elongation at yield were measured at roomtemperature (approximately 20° C.) on the film samples using a MTSSintech tensile test instrument following procedures set forth in ASTMStandard D882-97. Young's modulus is defined as the steepest slope ofthe beginning of the stress-strain curve. Films were tested at anelongation rate of 2.5 cm/min with the initial gauge length of 5.1 cm.The results are shown in Table 4.

TABLE 4 Young's Modulus, Tensile Strength, and Elongation of FilmSamples Young's Tensile Strength Sample Modulus (MPa) (MPa) Elongation(%) 1 0.72 0.51 137.9 2 0.57 0.44 173 3 1.0 0.86 132.8 4 0.71 0.45 122.35 0.72 0.56 157.4 6 0.33 0.33 311.9

Primary Coating—Properties—In Situ Modulus. In situ modulus measurementsof primary coating composition Samples 2, 3, and 5 were completed. Insitu modulus measurements require forming the primary coatings on aglass fiber having a diameter of 125 μm. Each of Samples 2, 3, and 5 wasseparately applied as a primary coating composition to a glass fiber asthe glass fiber was being drawn. The fiber draw speed was 50 m/s. Theprimary coating compositions were cured using a stack of five LEDsources. Each LED source was operated at 395 nm and had an intensity of12 W/cm². After application and curing of the primary coatingcompositions, a secondary coating composition was applied to each of thecured primary coatings and cured using UV sources to form a secondarycoating layer. The thickness of the primary coating was 32.5 μm and thethickness of the secondary coating was 26.0 μm.

The in situ modulus was measured using the following procedure. Asix-inch sample of fiber was obtained and a one-inch section from thecenter of the fiber was window stripped and wiped with isopropylalcohol. The window-stripped fiber was mounted on a sampleholder/alignment stage equipped with 10 mm×5 mm rectangular aluminumtabs that were used to affix the fiber. Two tabs were orientedhorizontally and positioned so that the short 5 mm sides were facingeach other and separated by a 5 mm gap. The window-stripped fiber waslaid horizontally on the sample holder across the tabs and over the gapseparating the tabs. The coated end of one side of the window-strippedregion of the fiber was positioned on one tab and extended halfway intothe 5 mm gap between the tabs. The one-inch window-stripped regionextended over the remaining half of the gap and across the opposing tab.After alignment, the sample was moved and a small dot of glue wasapplied to the half of each tab closest to the 5 mm gap. The fiber wasthen returned to position and the alignment stage was raised until theglue just touched the fiber. The coated end was then pulled away fromthe gap and through the glue such that the majority of the 5 mm gapbetween the tabs was occupied by the window-stripped region of thefiber. The portion of the window-stripped region remaining on theopposing tab was in contact with the glue. The very tip of the coatedend was left to extend beyond the tab and into the gap between the tabs.This portion of the coated end was not embedded in the glue and was theobject of the in situ modulus measurement. The glue was allowed to drywith the fiber sample in this configuration to affix the fiber to thetabs. After drying, the length of fiber fixed to each of the tabs wastrimmed to 5 mm. The coated length embedded in glue, the non-embeddedcoated length (the portion extending into the gap between the tabs), andthe primary diameter were measured.

The in situ modulus measurements were performed on a Rheometrics DMTA IVdynamic mechanical testing apparatus at a constant strain of 9e-6 1/sfor a time of forty-five minutes at room temperature (21° C.). The gaugelength was 15 mm. Force and the change in length were recorded and usedto calculate the in situ modulus of the primary coating. The tab-mountedfiber samples were prepared by removing any epoxy from the tabs thatwould interfere with the 15 mm clamping length of the testing apparatusto insure that there was no contact of the clamps with the fiber andthat the sample was secured squarely to the clamps. The instrument forcewas zeroed out. The tab to which the non-coated end of the fiber wasaffixed was then mounted to the lower clamp (measurement probe) of thetesting apparatus and the tab to which the coated end of the fiber wasaffixed was mounted to the upper (fixed) clamp of the testing apparatus.The test was then executed and the sample was removed once the analysiswas completed.

The in situ modulus of primary coating Samples 2, 3, and 5 are listed inTable 5.

TABLE 5 In Situ Modulus of Selected Primary Coatings Sample In-SituModulus (MPa) 2 0.27 3 0.33 5 0.3

Examples—Secondary Coatings

The following examples illustrate preparation of a representativesecondary coatings. Measurements of selected properties of therepresentative secondary coatings are also described.

Secondary Coating Compositions. Representative curable secondary coatingcompositions are listed in Table 6.

TABLE 6 Secondary Coating Compositions Composition Component KA KB KC KDSR601 (wt %) 72.0 30.0 30.0 30.0 SR602 (wt %) 37.0 37.0 37.0 SR349 (wt%) 30.0 15.0 SR399 (wt %) 15.0 SR499 (wt %) 30.0 CD9038 (wt %) 10.0Photomer 3016 (wt %) 15.0 TPO (wt %) 1.5 Irgacure 184 (wt %) 1.5Irgacure 1850 (wt %) 3.0 3.0 3.0 Irganox 1035 (pph) 0.5 DC-190 (pph) 1.0SR601 is ethoxylated (4) bisphenol A diacrylate (a monomer). SR602 isethoxylated (10) bisphenol A diacrylate (a monomer). SR349 isethoxylated (2) bisphenol A diacrylate (a monomer). SR399 isdipentaerythritol pentaacrylate. SR499 is ethoxylated (6)trimethylolpropane triacrylate. CD9038 is ethoxylated (30) bisphenol Adiacrylate (a monomer). Photomer 3016 is bisphenol A epoxy diacrylate (amonomer). TPO is a photoinitiator. Irgacure 184 is1-hydroxycyclohexylphenyl ketone (a photoinitiator). Irgacure 1850 isbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (aphotoinitiator). Irganox 1035 is thiodiethylenebis(3,5-di-tert-butyl)-4-hydroxyhydrocinnamate (an antioxidant). DC190is silicone-ethylene oxide/propylene oxide copolymer (a slip agent). Theconcentration unit “pph” refers to an amount relative to a basecomposition that includes all monomers, oligomers, and photoinitiators.For example, for secondary coating composition KA, a concentration of1.0 pph for DC-190 corresponds to 1 g DC-190 per 100 g combined ofSR601, CD9038, Photomer 3016, TPO, and Irgacure 184.

A comparative curable secondary coating composition (A) and threerepresentative curable secondary coating compositions (SB, SC, and SD)are listed in Table 7.

TABLE 7 Secondary Coating Compositions Composition Component A SB SC SDPE210 (wt %) 15.0 15.0 15.0 15.0 M240 (wt %) 72.0 72.0 72.0 62.0 M2300(wt %) 10.0 — — — M3130 (wt %) — 10.0 — — M370 (wt %) — — 10.0 10.0 TPO(wt %) 1.5 1.5 1.5 1.5 Irgacure 184 (wt %) 1.5 1.5 1.5 1.5 Irganox 1035(pph) 0.5 0.5 0.5 0.5 DC-190 (pph) 1.0 1.0 1.0 1.0PE210 is bisphenol-A epoxy diacrylate (available from Miwon SpecialtyChemical, Korea), M240 is ethoxylated (4) bisphenol-A diacrylate(available from Miwon Specialty Chemical, Korea), M2300 is ethoxylated(30) bisphenol-A diacrylate (available from Miwon Specialty Chemical,Korea), M3130 is ethoxylated (3) trimethylolpropane triacrylate(available from Miwon Specialty Chemical, Korea), TPO (a photoinitiator)is (2,4,6-trimethylbenzoyl)diphenyl phosphine oxide (available fromBASF), Irgacure 184 (a photoinitiator) is 1-hydroxycyclohexylphenylketone (available from BASF), Irganox 1035 (an antioxidant) isbenzenepropanoic acid,3,5-bis(1,1-dimethylethyl)-4-hydroxythiodi-2,1-ethanediyl ester(available from BASF). DC190 (a slip agent) is silicone-ethyleneoxide/propylene oxide copolymer (available from Dow Chemical). Theconcentration unit “pph” refers to an amount relative to a basecomposition that includes all monomers and photoinitiators. For example,for secondary coating composition A, a concentration of 1.0 pph forDC-190 corresponds to 1 g DC-190 per 100 g combined of PE210, M240,M2300, TPO, and Irgacure 184.

Secondary Coating—Properties. The Young's modulus, tensile strength atbreak, and elongation at break of secondary coatings made fromrepresentative secondary compositions A, KA, KB, KC, KD, SB, SC and SDwere measured.

Secondary Coating—Properties—Measurement Techniques. Properties ofsecondary coatings were determined using the measurement techniquesdescribed below:

Tensile Properties. The curable secondary coating compositions werecured and configured in the form of cured rod samples for measurement ofYoung's modulus, tensile strength at yield, yield strength, andelongation at yield. The cured rods were prepared by injecting thecurable secondary composition into Teflon® tubing having an innerdiameter of about 0.025″. The rod samples were cured using a Fusion Dbulb at a dose of about 2.4 J/cm² (measured over a wavelength range of225-424 nm by a Light Bug model IL390 from International Light). Aftercuring, the Teflon® tubing was stripped away to provide a cured rodsample of the secondary coating composition. The cured rods were allowedto condition for 18-24 hours at 23° C. and 50% relative humidity beforetesting. Young's modulus, tensile strength at break, yield strength, andelongation at yield were measured using a Sintech MTS Tensile Tester ondefect-free rod samples with a gauge length of 51 mm, and a test speedof 250 mm/min. Tensile properties were measured according to ASTMStandard D882-97. The properties were determined as an average of atleast five samples, with defective samples being excluded from theaverage.

Puncture Resistance of Secondary Coating. Puncture resistancemeasurements were made on samples that included a glass fiber, a primarycoating, and a secondary coating. The glass fiber had a diameter of 125μm. The primary coating was formed from the reference primary coatingcomposition listed in Table 8 below. Samples with various secondarycoatings were prepared as described below. The thicknesses of theprimary coating and secondary coating were adjusted to vary thecross-sectional area of the secondary coating as described below. Theratio of the thickness of the secondary coating to the thickness of theprimary coating was maintained at about 0.8 for all samples.

The puncture resistance was measured using the technique described inthe article entitled “Quantifying the Puncture Resistance of OpticalFiber Coatings”, by G. Scott Glaesemann and Donald A. Clark, publishedin the Proceedings of the 52^(nd) International Wire & Cable Symposium,pp. 237-245 (2003). A summary of the method is provided here. The methodis an indentation method. A 4-centimeter length of optical fiber wasplaced on a 3 mm-thick glass slide. One end of the optical fiber wasattached to a device that permitted rotation of the optical fiber in acontrolled fashion. The optical fiber was examined in transmission under100× magnification and rotated until the secondary coating thickness wasequivalent on both sides of the glass fiber in a direction parallel tothe glass slide. In this position, the thickness of the secondarycoating was equal on both sides of the optical fiber in a directionparallel to the glass slide. The thickness of the secondary coating inthe directions normal to the glass slide and above or below the glassfiber differed from the thickness of the secondary coating in thedirection parallel to the glass slide. One of the thicknesses in thedirection normal to the glass slide was greater and the other of thethicknesses in the direction normal to the glass slide was less than thethickness in the direction parallel to the glass slide. This position ofthe optical fiber was fixed by taping the optical fiber to the glassslide at both ends and is the position of the optical fiber used for theindentation test.

Indentation was carried out using a universal testing machine (Instronmodel 5500R or equivalent). An inverted microscope was placed beneaththe crosshead of the testing machine. The objective of the microscopewas positioned directly beneath a 75° diamond wedge indenter that wasinstalled in the testing machine. The glass slide with taped fiber wasplaced on the microscope stage and positioned directly beneath theindenter such that the width of the indenter wedge was orthogonal to thedirection of the optical fiber. With the optical fiber in place, thediamond wedge was lowered until it contacted the surface of thesecondary coating. The diamond wedge was then driven into the secondarycoating at a rate of 0.1 mm/min and the load on the secondary coatingwas measured. The load on the secondary coating increased as the diamondwedge was driven deeper into the secondary coating until punctureoccurred, at which point a precipitous decrease in load was observed.The indentation load at which puncture was observed was recorded and isreported herein as grams of force. The experiment was repeated with theoptical fiber in the same orientation to obtain ten measurement points,which were averaged to determine a puncture resistance for theorientation. A second set of ten measurement points was taken byrotating the orientation of the optical fiber by 180°.

Microbending. In the wire-mesh-covered drum test, the attenuation oflight at wavelength of 1550 nm through a coated fiber having a length of750 m was determined at room temperature. The microbend inducedattenuation was determined by the difference between a zero-tensiondeployment and a high-tension deployment on the wire-mesh-covered drum.Separate measurements were made for two winding configurations. In thefirst configuration, the fiber was wound in a zero-tension configurationon an aluminum drum having a smooth surface and a diameter ofapproximately 400 mm. The zero-tension winding configuration provided astress-free reference attenuation for light passing through the fiber.After sufficient dwell time, an initial attenuation measurement wasperformed. In the second winding configuration, the fiber sample waswound to an aluminun drum that was wrapped with fine wire mesh. For thisdeployment, the barrel surface of the aluminum drum was covered withwire mesh and the fiber was wrapped around the wire mesh. The mesh waswrapped tightly around the barrel without stretching and was kept intactwithout holes, dips, tearing, or damage. The wire-mesh material used inthe measurements was made from corrosion-resistant type 304 stainlesssteel woven wire cloth and had the following characteristics: mesh perlinear inch: 165×165, wire diameter: 0.0019″, width opening: 0.0041″,and open area %: 44.0. A 750 m length of coated fiber was wound at 1 m/son the wire-mesh-covered drum at 0.050 cm take-up pitch while applying80 (+/−1) grams of tension. The ends of the fiber were taped to maintaintension and there were no fiber crossovers. The points of contact of thewound fiber with the mesh impart stress to the fiber and the attenuationof light through the wound fiber is a measure of stress-induced(microbending) losses of the fiber. The wire-mesh-covered drummeasurement was performed after a dwell time of 1-hour. The increase infiber attenuation (in dB/km) in the measurement performed in the secondconfiguration (wire-mesh-covered drum) relative to the firstconfiguration (smooth drum) was determined for each wavelength. Theaverage of three trials was determined at each wavelength and isreported as the wire-mesh-covered drum microbend loss.

Reference Primary Coating. In measurements of in situ glass transitiontemperature (T_(g)), and puncture resistance, the measurement samplesincluded a primary coating between the glass fiber and a secondarycoating. The primary coating composition had the formulation given inTable 8 and is typical of commercially available primary coatingcompositions.

TABLE 8 Reference Primary Coating Composition Component AmountOligomeric Material  50.0 wt % SR504  46.5 wt % NYC  2.0 wt % TPO  1.5wt % Irganox 1035  1.0 pph 3-Acryloxypropyl  0.8 pph trimethoxysilanePentaerythritol 0.032 pph tetrakis(3-mercapto propionate)where the oligomeric material was prepared as described above fromH12MDI, HEA, and PPG4000 using a molar ratio n:m:p=3.5:3.0:2.0, SR504 isethoxylated(4)nonylphenol acrylate (available from Sartomer), NVC isN-vinylcaprolactam (available from Aldrich), TPO (a photoinitiator) is(2,4,6-trimethylbenzoyl)-diphenyl phosphine oxide (available from BASF),Irganox 1035 (an antioxidant) is benzenepropanoic acid,3,5-bis(1,1-dimethylethyl)-4-hydroxythiodi-2,1-ethanediyl ester(available from BASF), 3-acryloxypropyl trimethoxysilane is an adhesionpromoter (available from Gelest), and pentaerythritoltetrakis(3-mercaptopropionate) (also known as tetrathiol, available fromAldrich) is a chain transfer agent. The concentration unit “pph” refersto an amount relative to a base composition that includes all monomers,oligomers, and photoinitiators. For example, a concentration of 1.0 pphfor Irganox 1035 corresponds to 1 g Irganox 1035 per 100 g combined ofoligomeric material, SR504, NVC, and TPO.

Secondary Coatings—Properties—Tensile Properties. The results of tensileproperty measurements prepared from the representative curable secondarycompositions are shown in Table 9.

TABLE 9 Tensile Properties of Secondary Coatings Tensile Yield Young'sStrength Elongation Strength Modulus Composition (MPa) at yield (%)(MPa) (MPa) KA 54.3 39.0 1528 KB 63.1 24.1 1703 KC 45.7 28.4 1242 KD61.8 32.5 1837 A 86.09 4.60 48.21 2049 SB 75.56 4.53 61.23 2532 SC 82.024.76 66.37 2653 SD 86.08 4.87 70.05 2776

The results show that secondary coatings prepared from compositions SB,SC, and SD exhibited higher Young's modulus, and higher yield strengththan the secondary coating prepared from comparative composition A. Thehigher values represent improvements that make secondary coatingsprepared for the representative curable coating compositions disclosedherein better suited for small diameter optical fibers. Morespecifically, the higher values enable use of thinner secondary coatingson optical fibers without sacrificing performance. Thinner secondarycoatings reduce the overall diameter of the optical fiber and providehigher fiber counts in cables of a given cross-sectional area.

The Young's modulus of secondary coatings prepared as cured productsfrom the representative curable secondary coating compositions disclosedherein is greater than 1600 MPa, or greater than 1900 MPa, or greaterthan 2200 MPa, or greater than 2500 MPa, or in the range from 1600 MPato 2800 MPa, or in the range from 1900 MPa to 2500 MPa.

The yield strength of secondary coatings prepared as cured products fromthe representative curable secondary coating compositions disclosedherein is greater than 55 MPa, or greater than 60 MPa, or greater than65 MPa, or greater than 70 MPa, or in the range from 55 MPa to 75 MPa,or in the range from 60 MPa to 70 MPa.

Secondary Coatings—Properties—Puncture Resistance. The punctureresistance of secondary coatings made from comparative curable secondarycoating composition A, a commercial curable secondary coatingcomposition (CPC6e) from a commercial vendor (DSM Desotech) having aproprietary composition, and curable secondary coating composition SDwas determined according to the method described above. Several fibersamples with each of the three secondary coatings were prepared. Eachfiber sample included a glass fiber with a diameter of 125 μm, a primarycoating formed from the reference primary coating composition listed inTable 8, and one of the three secondary coatings. Samples with varioussecondary coatings were prepared. The thicknesses of the primary coatingand secondary coating were adjusted to vary the cross-sectional area ofthe secondary coating as shown in FIG. 7. The ratio of the thickness ofthe secondary coating to the thickness of the primary coating wasmaintained at about 0.8 for all samples.

Fiber samples with a range of thicknesses were prepared for each of thesecondary coatings to determine the dependence of puncture load on thethickness of the secondary coating. One strategy for achieving higherfiber count in cables is to reduce the thickness of the secondarycoating. As the thickness of the secondary coating is decreased,however, its performance diminishes and its protective function iscompromised. Puncture resistance is a measure of the protective functionof a secondary coating. A secondary coating with a high punctureresistance withstands greater impact without failing and provides betterprotection for the glass fiber.

The puncture load as a function of cross-sectional area for the threecoatings is shown in FIG. 7. Cross-sectional area is selected as aparameter for reporting puncture load because an approximately linearcorrelation of puncture load with cross-sectional area of the secondarycoating was observed. Traces 72, 74, and 76 shows the approximate lineardependence of puncture load on cross-sectional area for the comparativesecondary coatings obtained by curing the comparative CPC6e secondarycoating composition, the comparative curable secondary coatingcomposition A, and curable secondary coating composition SD;respectively. The vertical dashed lines are provided as guides to theeye at cross-sectional areas of 10000 μm², 15000 μm², and 20000 μm² asindicated.

The CPC6e secondary coating depicted in Trace 72 corresponds to aconventional secondary coating known in the art. The comparativesecondary coating A depicted in Trace 74 shows an improvement inpuncture load for high cross-sectional areas. The improvement, however,diminishes as the cross-sectional area decreases. This indicates that asecondary coating obtained as a cured product from comparative curablesecondary coating composition A is unlikely to be suitable for lowdiameter, high fiber count applications. Trace 76, in contrast, shows asignificant increase in puncture load for the secondary coating obtainedas a cured product from curable secondary coating composition SD. At across-sectional area of 7000 μm², for example, the puncture load of thesecondary coating obtained from curable secondary coating composition SDis 50% or more greater than the puncture load of either of the other twosecondary coatings.

The puncture load of secondary coatings formed as cured products of thecurable secondary coating compositions disclosed herein at across-sectional area of 10000 μm² is greater than 36 g, or greater than40 g, or greater than 44 g, or greater than 48 g, or in the range from36 g to 52 g, or in the range from 40 g to 48 g. The puncture load ofsecondary coatings formed as cured products of the curable secondarycoating compositions disclosed herein at a cross-sectional area of 15000μm² is greater than 56 g, or greater than 60 g, or greater than 64 g, orgreater than 68 g, or in the range from 56 g to 72 g, or in the rangefrom 60 g to 68 g. The puncture load of secondary coatings formed ascured products of the curable secondary coating compositions disclosedherein at a cross-sectional area of 20000 μm² is greater than 68 g, orgreater than 72 g, or greater than 76 g, or greater than 80 g, or in therange from 68 g to 92 g, or in the range from 72 g to 88 g. Embodimentsinclude secondary coatings having any combination of the foregoingpuncture loads.

As used herein, normalized puncture load refers to the ratio of punctureload to cross-sectional area. The puncture load of secondary coatingsformed as cured products of the curable secondary coating compositionsdisclosed herein have a normalized puncture load greater than 3.0×10⁻³g/μm², or greater than 3.5×10⁻³ g/μm², or greater than 4.0×10⁻³ g/μm²,or greater than 4.5×10⁻³ g/μm², or greater than 5.0×10⁻³ g/μm², or inthe range from 3.2×10⁻³ g/μm² to 5.6×10⁻³ g/μm², or in the range from3.5×10⁻³ g/μm² to 5.2×10⁻³ g/μm², or in the range from 4.0×10⁻³ g/μm² to4.8×10⁻³ g/μm².

Examples—Relative Refractive Index Profile

The following examples illustrate representative relative refractiveindex profiles and optical properties of optical fibers having lowmacrobend loss. The relative refractive index profiles are shown inFIGS. 8A and 8B. Profile 1, Profile 2, and Profile 3 are shown. Eachprofile includes, in order of increasing radial position beginning atthe centerline (r=0), a core region, an inner cladding region, anintermediate cladding region, and an outer cladding region. The outercladding region extends to a radius r₄=40.0 μm (not shown). The coreregion of each of the three profiles is silica glass doped with alkali.The inner cladding region, intermediate cladding region, and outercladding region of each of the three profiles is silica glass doped withfluorine. The fluorine doping concentration is highest in theintermediate cladding region and lower in the inner cladding region andouter cladding region.

Macrobending. The macrobend loss at 1550 nm of optical fibers with eachof the three profiles was calculated for mandrels of a variousdiameters. Macrobend loss is denoted by “BLDM,” where “DM” is thediameter in mm of the mandrel used to assess macrobending performance.The diameter DM is also referred to herein as “macrobend diameter”. Themacrobending performance as discussed herein is gauged by characterizingthe induced attenuation increase in a mandrel wrap test unless otherwisenoted. The mandrel wrap test is specified in TIA-455-62: FOTP-62IEC-60793-1-47 Optical Fibres—Part 1-47: Measurement Methods and TestProcedures—Macrobending Loss, by Telecommunications Industry Association(TIA). In the mandrel wrap test, the optical fiber is wrapped one ormore times around a smooth cylindrical mandrel of diameter DM, and theincrease in attenuation at a specified wavelength due to the bending isdetermined. Attenuation in the mandrel wrap test is expressed in unitsof dB/turn, where one turn refers to one revolution of the optical fiberabout the mandrel. Bend loss values for mandrel diameters of 15 mm, 20mm and 30 mm, i.e., for BL₁₅, BL₂₀ and BL₃₀, are provided below.

Bend loss and selected optical properties of each of the three profilesare summarized in Table 10. In Table 10, “MFD” refers to mode fielddiameter, λ₀ refers to the zero dispersion wavelength, λ_(CC) refers tothe cable cutoff wavelength, and V_(Trench) refers to trench volume.

TABLE 10 Properties of Optical Fibers Profile 1 Profile 2 Profile 3 MFDat 1310 nm (μm) 9.22 9.07 9.39 MFD at 1550 nm (μm) 10.27 10.08 10.48 MFDat 1625 nm (μm) 10.61 10.41 10.83 λ₀ (nm) 1319 1319 1320 λ_(CC) (nm)1315 1419 1339 V_(Trench) (% Δμm²) 54.5 55 55 BL₁₅ (dB/turn) 0.04 0.01370.042 BL₂₀ (dB/turn) 0.009 0.0003 0.009 BL₃₀ (dB/turn) 0.001 0.00020.001

The macrobend loss of the optical fiber at a wavelength of 1550 nm, whenwrapped around a mandrel having a diameter of 30 mm, is less than 0.010dB/turn, or less than 0.005 dB/turn, or less than 0.002 dB/turn, or lessthan 0.001 dB/turn, or less than 0.00005 dB/turn. The macrobend loss ofthe optical fiber at a wavelength of 1550 nm, when wrapped around amandrel having a diameter of 20 mm, is less than 0.100 dB/turn, or lessthan 0.050 dB/turn, or less than 0.010 dB/turn, or less than 0.005dB/turn, or less than 0.001 dB/turn, or less than 0.0005 dB/turn. Themacrobend loss of the optical fiber at a wavelength of 1550 nm, whenwrapped around a mandrel having a diameter of 15 mm, is less than 0.500dB/turn, or less than 0.100 dB/turn, or less than 0.050 dB/turn, or lessthan 0.040 dB/turn, or less than 0.030 dB/turn, or less than 0.020dB/turn, or less than 0.015 dB/turn.

The wire-mesh-covered drum microbending loss at 1550 nm is less than 1.0dB/km, or less than 0.75 dB/km, or less than 0.50 dB/km, or less than0.25 dB/km, or less than 0.10 dB/km, or less than 0.05 dB/km, or lessthan 0.03 dB/km, or in the range from 0.01 dB/km to 1.0 dB/km, or in therange from 0.02 dB/km to 0.50 dB/km, or in the range from 0.03 dB/km to0.25 dB/km, or in the range from 0.04 dB/km to 0.15 dB/km.

Examples—Reduced Radius Optical Fibers

The following examples illustrate optical fibers with reduced radiusthat exhibit high mechanical reliability and low microbend loss.Conventional optical fibers include a glass fiber with radius r₄=62.5μm, a primary coating with a thickness r₅−r₄=32.5 μm, and a secondarycoating with a thickness r₆−r₅=26 μm. The radius r₆ of a conventionaloptical fiber is 121 μm (diameter 2r₆=242 μm). The exemplary opticalfibers disclosed in the examples that follow have a radius r₆ less thanor equal to 100 μm. The reduced radius of the exemplary optical fibersis achieved by reducing one or more of the radius r₄ of the glass fiber,the thickness r₅−r₄ of the primary coating, or the thickness r₆−r₅ ofthe secondary coating relative to a conventional optical fiber.

Table 11 summarizes selected properties of a series of comparativeoptical fibers (labeled CE1, CE2, CE3, CE4, and CE5) and Table 12summarizes selected properties of a series of exemplary optical fibersin accordance with the present disclosure (labeled Ex. 1, Ex. 2, Ex. 3,Ex. 4, Ex. 5, and Ex. 6). Tables 11 and 12 list the glass fiber radiusr₄, the in situ modulus of the primary coating (E_(p)), the radius r₅ ofthe primary coating, the thickness r₅−r₄ of the primary coating, thespring constant χ_(p) of a primary coating, the Young's modulus of thesecondary coating (E_(s)), the radius r₆ of the secondary coating, thethickness r₆−r₅ of the secondary coating, the cross-sectional area ofthe secondary coating (As), and the ratio of the thickness r₅−r₄ of theprimary coating to the thickness r₆−r₅ of the secondary coating(R_(ps)).

TABLE 11 Comparative Optical Fiber Samples CE1 CE2 CE3 CE4 CE5 r₄ (μm)62.5 62.5 62.5 62.5 40.25 E_(p) (MPa) 0.20 0.25 0.40 0.20 0.40 r₅ (μm)95 95 95 80 80 r₅-r₄ (μm) 32.5 32.5 32.5 17.5 39.75 χ_(p) (MPa) 0.770.96 1.54 1.43 0.81 E_(s) (MPa) 1948 1882 1200 1948 1200 r₆ (μm) 121 121121 100 100 r₆-r₅ (μm) 26 26 26 20 20 A_(x) (μm²) 17643 17643 1764311310 11310 R_(ps) 1.25 1.25 1.25 0.88 1.99

Comparative optical fibers CE1, CE2, and CE3 have a glass fiber radiusr₄, a thickness r₅−r₄ of the primary coating, and a thickness r₆−r₅ ofthe secondary coating consistent with conventional optical fibers. Theradius r₆ of comparative optical fibers CE1, CE2, and CE3 defines thecurrent standard for fiber density in cables. To increase fiber densityin cables, optical fibers with lower values of r₆ are desired. Suchreduced radius fibers must, however, provide high mechanical reliabilitywhile maintaining low macrobend and microbend loss.

Comparative optical fiber CE4 is a reduced radius variation ofcomparative optical fiber CE1. The mechanical properties (E_(p), E_(s),and χ_(p)) of the coatings of comparative optical fiber CE4 are the sameas for comparative optical fiber CE1. Comparative optical fiber CE4 is areduced radius optical fiber obtained by reducing the thickness r₅−r₄ ofthe primary coating to and the thickness r₆−r₅ of the secondary coatingrelative to comparative optical fiber CE1. Although the overall radiusof the optical fiber is reduced, the spring constant χ_(p) of theprimary coating of comparative optical fiber CE4 is too high (too stiff)to adequately protect the glass fiber from external force applied to theexterior of the optical fiber. The high spring constant χ_(p) of theprimary coating leads to strong coupling the secondary coating to theglass fiber and weak dampening of force by the primary coating.Microbending losses are accordingly high.

Comparative optical fiber CE5 is a reduced radius variation ofcomparative optical fiber CE3. The mechanical properties (E_(p), E_(s),and χ_(p)) of the coatings of comparative optical fiber CE5 are the sameas for comparative optical fiber CE3. Comparative optical fiber CE5 is areduced radius optical fiber obtained by reducing the radius r₄ of theglass fiber and the thickness r₆−r₅ of the secondary coating relative tocomparative optical fiber CE3. The thickness r₅−r₄ of the primarycoating is increased in comparative optical fiber CE5 relative tocomparative optical fiber CE3 to reduce the spring constant χ_(p) of theprimary coating. Although the overall radius of the optical fiber isreduced and the spring constant χ_(p) of the primary coating is reduced,the Young's modulus of comparative fiber CE5 is too low to provide highpuncture resistance and too low to adequately attenuate transmission ofexternal forces to the primary coating. As a result, mechanicalreliability is poor and microbending losses are high.

TABLE 12 Exemplary Optical Fiber Samples Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5Ex. 6 r₄ (μm) 40.25 40.25 40.25 40.25 40.25 40.25 E_(p) (MPa) 0.20 0.250.20 0.20 0.20 0.25 r₅ (μm) 80 80 75 71 70 70 r₅ − r₄ (μm) 39.75 39.7534.75 30.75 29.75 29.75 χ_(p) (MPa) 0.41 0.51 0.46 0.52 0.54 0.68 E_(s)(MPa) 1948 1882 1948 1948 1948 1882 r₆ (μm) 100 100 100 100 90 90 r₆ −r₅ (μm) 20 20 25 29 20 20 A_(x) (μm²) 11310 11310 13744 15579 1005310053 R_(ps) 1.99 1.99 1.39 1.06 1.49 1.49

The exemplary optical fibers are configured to possess a reduced radiusr₆ relative to conventional optical fibers, while still achieving bothlow microbend loss and high mechanical reliability. In particular, thespring constant χ_(p) of the primary coating is reduced relative to thecomparative optical fibers and low microbending loss are achieved as aresult. The increased Young's modulus E_(s) of the secondary coatingresists transmission of force through the secondary coating and reducesthe force that enters the primary coating. A synergistic relationshipbetween the Young's modulus of the secondary coating and the springconstant χ_(p) of the primary coating leads to both low microbendingloss and high puncture resistance in a reduced radius optical fiber.

In preferred embodiments, the spring constant χ_(p) of the primarycoating is less than 1.0 MPa, or less than 0.80 MPa, or less than 0.70MPa, or less than 0.60 MPa, or less than 0.50 MPa, or less than 0.40MPa, or in the range from 0.30 MPa to 0.90 MPa, or in the range from0.30 MPa to 0.80 MPa, or in the range from 0.30 MPa to 0.70 MPa, or inthe range from 0.30 MPa to 0.60 MPa, or in the range from 0.40 MPa to0.90 MPa, or in the range from 0.40 MPa to 0.80 MPa, or in the rangefrom 0.40 MPa to 0.70 MPa, or in the range from 0.40 MPa to 0.60 MPa.

In other preferred embodiments, the spring constant χ_(p) of the primarycoating is less than 1.0 MPa and the Young's modulus E_(s) of thesecondary coating is greater than 1600 MPa, the spring constant χ_(p) ofthe primary coating is less than 0.80 MPa and the Young's modulus E_(s)of the secondary coating is greater than 1700 MPa, the spring constantχ_(p) of the primary coating is less than 0.70 MPa and the Young'smodulus E_(s) of the secondary coating is greater than 1800 MPa, thespring constant χ_(p) of the primary coating is less than 0.60 MPa andthe Young's modulus E_(s) of the secondary coating is greater than 1900MPa, the spring constant χ_(p) of the primary coating is less than 0.50MPa and the Young's modulus E_(s) of the secondary coating is greaterthan 2000 MPa, the spring constant χ_(p) of the primary coating is inthe range from 0.30 MPa to 1.0 MPa and the Young's modulus E_(s) of thesecondary coating is in the range from 1600 MPa to 2800 MPa, the springconstant χ_(p) of the primary coating is in the range from 0.30 MPa to0.80 MPa and the Young's modulus E_(s) of the secondary coating is inthe range from 1700 MPa to 2800 MPa, the spring constant χ_(p) of theprimary coating is in the range from 0.30 MPa to 0.70 MPa and theYoung's modulus E_(s) of the secondary coating is in the range from 1800MPa to 2800 MPa, the spring constant χ_(p) of the primary coating is inthe range from 0.30 MPa to 0.60 MPa and the Young's modulus E_(s) of thesecondary coating is in the range from 1900 MPa to 2800 MPa, the springconstant χ_(p) of the primary coating is in the range from 0.40 MPa to1.0 MPa and the Young's modulus E_(s) of the secondary coating is in therange from 1600 MPa to 2800 MPa, the spring constant χ_(p) of theprimary coating is in the range from 0.40 MPa to 0.80 MPa and theYoung's modulus E_(s) of the secondary coating is in the range from 1700MPa to 2800 MPa, the spring constant χ_(p) of the primary coating is inthe range from 0.40 MPa to 0.70 MPa and the Young's modulus E_(s) of thesecondary coating is in the range from 1800 MPa to 2800 MPa, the springconstant χ_(p) of the primary coating is in the range from 0.40 MPa to0.60 MPa and the Young's modulus E_(s) of the secondary coating is inthe range from 1900 MPa to 2800 MPa.

The ratio R_(ps) of the thickness r₅−r₄ of the primary coating to thethickness r₆−r₅ of the secondary coating is in the range from 0.80 to2.20, or in the range from 0.85 to 1.85, or in the range from 0.90 to1.50, or in the range from 0.95 to 1.30.

Examples—Reduced Radius Optical Fibers

Further illustrative examples of reduced radius optical fibers aresummarized in FIG. 9 and in Tables 13 and 14. Each of the reduced radiusoptical fibers has a relative refractive index profile with anintermediate cladding region surrounding and directly adjacent to thecore region and an outer cladding region surrounding and directlyadjacent to the intermediate cladding region. Table 13 summarizesselected properties of a series of comparative optical fibers (labeledC1, C2, and C3) and two exemplary optical fibers in accordance with thepresent disclosure (labeled Ex. 7 and Ex. 8). Table 13 lists the radiusr₁ and the average relative refractive index Δ₁ of the core region, theradius r₃, relative refractive index Δ₃, and trench volume V_(Trench)(=V₃) of the intermediate cladding region, the radius r₄ and relativerefractive index Δ₄ of the outer cladding region, the radius r₅ of theprimary coating, the thickness r₅−r₄ of the primary coating, the radiusr₆ of the secondary coating, the thickness r₆−r₅ of the secondarycoating, the cross-sectional area of the secondary coating (As), and theratio of the thickness r₅−r₄ of the primary coating to the thicknessr₆−r₅ of the secondary coating (R_(ps)). The same primary coating withthe same composition and the same modulus, and the same secondarycoating with the same composition and same modulus, were used for theoptical fibers listed in Tables 13 and 14.

TABLE 13 Exemplary Optical Fiber Samples - Profiles C1 C2 C3 Ex. 7 Ex. 8r₁ (μm) 6.11 5.92 6.11 5.92 5.74 Δ₁ (%) −0.028 −0.026 −0.025 −0.026−0.026 r₃ (μm) 19.64 18.77 19.01 19.15 19.24 Δ₃ (%) −0.420 −0.411 −0.423−0.425 −0.431 V_(Trench) (% Δμm²) −1.77 26.22 20.44 21.63 17.89 r₄ (μm)40.25 40.25 40.25 40.25 40.25 Δ₄ (%) −0.434 −0.333 −0.367 −0.367 −0.388r₅ (μm) 62.5 62.5 62.5 80.0 80.0 r₅-r₄ (μm) 22.25 22.25 22.25 39.7539.75 r₆ (μm) 80.0 80.0 80.0 100.0 100.0 r₆-r₅ (μm) 17.5 17.5 17.5 20.020.0 A_(x) (μm²) 31337 31337 31337 45239 45239 R_(ps) 1.27 1.27 1.271.99 1.99

Table 14 shows selected performance attributes of comparative opticalfibers C1, C2, and C3, and exemplary optical fibers Ex. 7 and Ex. 8.Attributes listed in Table 14 are the cable cutoff wavelength λ_(CC),mode field diameter (MFD) at 1550 nm, effective area A_(eff) at 1550 nm,and attenuation at 1550 nm and 1625 nm.

TABLE 14 Exemplary Optical Fiber Samples C1 C2 C3 Ex. 7 Ex. 8 λ_(CC)(nm) 1525 ≤1134 ≤1233 1235 1430 MFD at 1550 nm (μm) 10.69 10.64 10.7310.72 A_(eff) at 1550 nm (μm²) 89.8 88.9 90.4 90.3 Attenuation at 1550nm 0.556 0.269 0.198 0.188 (dB/km) Attenuation at 1625 nm 1.444 0.4420.256 0.206 (dB/km)

The results shown in Table 14 show a clear improvement (reduction) inattenuation at both 1550 nm and 1625 nm for the two exemplary fibers.The reduction in attenuation reflects a reduction in microbending loss.The reduced attenuation is attributable primarily to proper selection ofthe thickness of the primary coating and trench volume. The thickness ofthe primary coatings of comparative examples C1, C2, and C3 is too lowto provide adequate resistance to microbending forces. Comparativeexample C1 lacks a trench. Instead, the average relative refractiveindex Δ₃ of the intermediate cladding region is greater than the averagerelative refractive index Δ₄ of the outer cladding region. This leads toa reporting of a negative value of V_(Trench) listed for comparativeexample C1, which in effect has an inverted trench and a relativerefractive index profile expected to exhibit high microbending losses.Comparative examples C2 and C3 have the same thickness of primarycoating and differ primarily with respect to trench volume. The trenchvolume of comparative sample C2 is higher than the trench volume ofcomparative example C3 and higher attenuation is observed. Exemplarysample Ex. 7 and comparative example C3 have similar trench volumes, butthe thicker primary coating of exemplary sample Ex. 7 leads to lowermicrobending loss and lower attenuation. Exemplary sample Ex. 8 has thesame thickness of primary coating as exemplary sample Ex. 7 and exhibitslower microbending loss and lower attenuation. While not wishing to bebound by theory, it is believed that the improvement in performance ofexemplary sample Ex. 8 is due to a smaller trench volume. It is notedthat for a given thickness of secondary coating, the cross-sectionalarea of the secondary coating also increases as the thickness of theprimary coating increases. A higher cross-sectional area for thesecondary coating improves puncture resistance of the secondary coatingand hence improves mechanical reliability of the optical fiber.

These examples indicate that microbending losses and attenuation inreduced radius optical fibers depend on the thickness of the primarycoating and the trench volume of the intermediate cladding region. Invarious embodiments, the thickness of the primary coating is in therange from 25.0 μm to 40.0 μm and the trench volume V_(Trench) of theintermediate cladding region is in the range from 10% Δμm² to 30% Δμm².

Examples—Attenuation

Modeled Results. FIG. 10 shows results of a model used to determineattenuation as a function of wavelength in two optical fibers.Attenuation is expressed in units of dB/km and represents intensity lossin the transmission of an optical signal through an optical fiber.Microbending loss is a significant contribution to attenuation. Theattenuation results shown as Traces 120 and 125 are based on a commonglass fiber having a radius r₄=40.25 μm, and on primary and secondarycoatings having the same composition and same in situ modulus E_(p)=0.2MPa and Young's modulus E_(s)=1948 MPa. Traces 120 and 125 differ in thethickness of the primary and secondary coatings. In Trace 120, theprimary coating has a radius r₅=62.5 μm and a thickness r₅−r_(4=22.25)μm, and the secondary coating has a radius r_(6=80.0) μm and a thicknessr₆−r₅=17.5 μm. In Trace 125, the primary coating has a radius r₅=80.0 μmand a thickness r₅−r_(4=39.75) μm, and the secondary coating has aradius r_(6=100.0) μm and a thickness r₆−r₅=20.0 μm. The results showthat the contribution of microbending to the attenuation loss aresignificantly reduced when the thickness of the primary coating isincreased. Results of the model indicate that a thickness r₅−r₄ of atleast 20.0 μm is needed to provide tolerable microbending losses atwavelengths near 1550 nm.

Examples—Load on Glass Fiber

Modeled Results. The experimental examples and principles disclosedherein indicate that by varying the mole numbers n, m, and p, it ispossible to control the relative amount of di-adduct compound in theoligomer as well as the properties of cured films formed from theprimary coating compositions over a wide range, including the rangesspecified herein for Young's modulus and in situ modulus of the primarycoating. Similarly, variations in the type and concentration ofdifferent monomers in the secondary composition leads to variations inthe Young's modulus over the range disclosed herein. Curing dose isanother parameter that can be used to vary modulus of primary andsecondary coatings formed from the curable compositions disclosedherein.

To examine the effect of the thickness and modulus of the primary andsecondary coatings on transmission of a radial force to a glass fiber, aseries of modeled examples was considered. In the model, a radialexternal load P was applied to the surface of the secondary coating ofan optical fiber and the resulting load at the surface of the glassfiber was calculated. The glass fiber was modeled with a Young's modulusof 73.1 GPa (consistent with silica glass) and a diameter of 125 μm. ThePoisson ratios v_(p) and v_(s) of the primary and secondary coatingswere fixed at 0.48 and 0.33, respectively. A comparative sample C4 andeleven samples M1-M11 in accordance with the present disclosure wereconsidered. The comparative sample included primary and secondarycoatings with thicknesses and moduli consistent with optical fibersknown in the art. Samples M1-M11 are examples with reduced thicknessesof the primary and/or secondary coatings. Parameters describing theconfigurations of the primary and secondary coatings are summarized inTable 15, where E_(p) is the in situ modulus of the primary coating, r₅is radius of the primary coating, r₅−r₄ is the thickness of the primarycoating, E_(s) is the Young's modulus of the secondary coating, r₆ isthe radius of the secondary coating, and r₆−r₅ is the thickness of thesecondary coating.

TABLE 15 Coating Properties of Modeled Optical Fibers Primary CoatingSecondary Coating E_(p) r₅ r₅ − r₄ E_(s) r₆ r₆ − r₅ Sample (MPa) (μm)(μm) (MPa) (μm) (μm) C4 0.16 95 32.5 2000 121 26 M1 0.18 81 23.5 1900100 19 M2 0.16 78.5 21 2000 95 16.5 M3 0.14 75.5 18 2000 90 14.5 M4 0.1173 15.5 2000 85 12 M5 0.20 80 25 1900 100 20 M6 0.19 77 22 2000 95 18 M70.16 74.5 19.5 2000 90 15.5 M8 0.13 71.5 16.5 2000 85 13.5 M9 0.22 7926.5 1900 100 21 M10 0.20 76 23.5 2000 95 19 M11 0.18 73.5 21 2000 9016.5

Table 16 summarizes the load P1 at the outer surface of the glass fiberas a fraction of load P applied to the surface of the secondary coating.The ratio P1/P is referred to herein as the load transfer parameter andcorresponds to the fraction of external load P transmitted through theprimary and secondary coatings to the surface of the glass fiber. Theload P is a radial load and the load transfer parameter P1/P wascalculated from a model based on Eqs. (11)-(13):

$\begin{matrix}{\frac{P_{1}}{P} = \frac{4\left( {1 - v_{p}} \right)\left( {1 - v_{s}} \right)}{\left\{ {A + B} \right\}}} & (11) \\{where} & \; \\{A = \left( \frac{{E_{s}\left( {1 + v_{p}} \right)}\left( {1 - {2v_{p}}} \right)\left( {1 - \left( {r_{4}/r_{5}} \right)^{2}} \right)\left( {1 - \left( {r_{5}/r_{6}} \right)^{2}} \right)}{E_{p}\left( {1 + v_{s}} \right)} \right)} & (12) \\{and} & \; \\{B = \left( {\left( {1 - {2{v_{p}\left( {r_{4}/r_{5}} \right)}^{2}} + \left( {r_{4}/r_{5}} \right)^{2}} \right)\left( {1 - {2{v_{s}\left( {r_{5}/r_{6}} \right)}^{2}} + \left( {r_{5}/r_{6}} \right)^{2}} \right)} \right)} & (13)\end{matrix}$

In Eqs. (11)-(13), v_(p) and v_(s) are the Poisson's ratios of theprimary and secondary coatings, r₄ is the radius of the glass fiber, r₅is the radius of the primary coating, r₆ is the radius of the secondarycoating, E_(p) is the in situ modulus of the primary coating, and E_(s)is the Young's modulus of the secondary coating. The scaled loadtransfer parameter P1/P (scaled) in Table 16 corresponds to the ratioP1/P for each sample relative to comparative sample C4.

TABLE 16 Load Transfer Parameter (P1/P) at Surface of Glass Fiber SampleP1/P P1/P (scaled) C4 0.00445 1.00 M1 0.00430 0.97 M2 0.00421 0.95 M30.00436 0.98 M4 0.00428 0.96 M5 0.00429 0.97 M6 0.00437 0.99 M7 0.004320.97 M8 0.00422 0.95 M9 0.00427 0.96 M10 0.00411 0.93 M11 0.00427 0.96

The modeled examples show that despite smaller coating thicknesses,optical fibers having primary and secondary coatings as described hereinexhibit a reduction in the force experienced by a glass fiber relativeto a comparative optical fiber having conventional primary and secondarycoatings with conventional thicknesses. The resulting reduction inoverall size of the optical fibers described herein enables higher fibercount in cables of a given size (or smaller cable diameters for a givenfiber count) without increasing the risk of damage to the glass fibercaused by external forces.

The scaled load transfer parameter P1/P (scaled) of the secondarycoating is less than 0.99, or less than 0.97, or less than 0.95. Theload transfer parameter P1/P of the secondary coating is less than0.00440, or less than 0.00436, or less than 0.00432, or less than0.00428, or less than 0.00424, or less than 0.00420, or less than0.00416, or less than 0.00412, or in the range from 0.00400 to 0.00440,or in the range from 0.00408 to 0.00436, or in the range from 0.00412 to0.00432, or in the range from 0.00416 to 0.00428, or in the range from0.00420 to 0.00424.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is no way intended thatany particular order be inferred.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the invention. Since modifications combinations,sub-combinations and variations of the disclosed embodimentsincorporating the spirit and substance of the invention may occur topersons skilled in the art, the invention should be construed to includeeverything within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. An optical fiber comprising: a core region, thecore region comprising silica glass doped with an alkali metal oxide,the core region having a radius r₁ in the range from 3.0 μm to 10.0 μmand a relative refractive index profile Δ₁ having a maximum relativerefractive index Δ_(1max) in the range from −0.15% to 0.30%; a claddingregion surrounding and directly adjacent to the core region, thecladding region having a radius r₄ in the range from 37.5 μm to 52.5 μm;a primary coating surrounding and directly adjacent to the claddingregion, the primary coating having a radius r₅, a spring constant χ_(p),an in situ modulus in the range from 0.05 MPa to 0.30 MPa and athickness r₅−r₄ in the range from 20.0 μm to 40.0 μm; and a secondarycoating surrounding and directly adjacent to the primary coating, thesecondary coating having a radius r₆ less than or equal to 100.0 μm, aYoung's modulus greater than 1600 MPa and a thickness r₆−r₅ in the rangefrom 15.0 μm to 30.0 μm.
 2. The optical fiber of claim 1, whereinΔ_(1max) is in the range from −0.05% to 0.15%.
 3. The optical fiber ofclaim 1, wherein the core comprises an inner core region and an outercore region, the inner core region having a radius r_(a) in the rangefrom 0.25 μm to 3.0 μm and the outer core region having the radius r₁.4. The optical fiber of claim 1, wherein the cladding comprises anintermediate cladding region and an outer cladding region surroundingand directly adjacent to the intermediate cladding region; theintermediate cladding region having a radius r₃ in the range from 10.0μm to 30.0 μm, a relative refractive index Δ₃ in the range from −0.30%to −0.90%; the outer cladding having the radius r₄ and a relativerefractive index Δ₄ in the range from −0.60% to 0.0%.
 5. The opticalfiber of claim 4, wherein the intermediate cladding region has athickness in the range from 5.0 μm to 20.0 μm.
 6. The optical fiber ofclaim 4, wherein the intermediate cladding region is directly adjacentto the core region.
 7. The optical fiber of claim 6, wherein theintermediate cladding region has a trench volume V_(Trench) in the rangefrom 10.0% Δμm² to 40.0% Δμm².
 8. The optical fiber of claim 4, whereinthe cladding region further comprises an inner cladding region, theinner cladding region surrounding and directly adjacent to the coreregion, the inner cladding region having a radius r₂ in the range from6.0 μm to 18.0 μm and a relative refractive index Δ₂ less than therelative refractive index Δ_(1max) and greater than the relativerefractive index Δ₃, the intermediate cladding region surrounding anddirectly adjacent to the inner cladding region.
 9. The optical fiber ofclaim 8, wherein the relative refractive index Δ₂ is in the range from−0.45% to −0.15% and wherein the inner cladding region has a thicknessr₂−r₁ in the range from 3.0 μm to 9.0 μm.
 10. The optical fiber of claim8, wherein the intermediate cladding region has a trench volumeV_(Trench) in the range from 20% Δμm² to 70% Δμm².
 11. The optical fiberof claim 4, wherein the relative refractive index Δ₄ is in the rangefrom −0.45% to −0.15%.
 12. The optical fiber of claim 1, wherein theradius r₄ is in the range from 37.5 μm to 47.5 μm.
 13. The optical fiberof claim 1, wherein the radius r₅ is less than or equal to 85.0 μm. 14.The optical fiber of claim 1, wherein the thickness r₅−r₄ is in therange from 25.0 μm to 37.5 μm.
 15. The optical fiber of claim 1, whereinthe spring constant χ_(p) is less than 0.50 MPa and the Young's modulusis greater than 2000 MPa.
 16. The optical fiber of claim 1, wherein theprimary coating is a cured product of a coating composition comprising:a radiation-curable monomer; an adhesion promoter, the adhesion promotercomprising an alkoxysilane compound or a mercapto-functional silanecompound; and an oligomer, the oligomer comprising: a polyether urethaneacrylate compound having the molecular formula:

wherein R₁, R₂ and R₃ are independently selected from linear alkylenegroups, branched alkylene groups, or cyclic alkylene groups; y is 1, 2,3, or 4; and x is between 40 and 100; and a di-adduct compound havingthe molecular formula:

wherein the di-adduct compound is present in an amount of at least 1.0wt % in the oligomer.
 17. The optical fiber of claim 1, wherein theradius r₆ is less than or equal to 90.0 μm.
 18. The optical fiber ofclaim 1, wherein the Young's modulus is greater than 2000 MPa.
 19. Theoptical fiber of claim 1, wherein the thickness r₆−r₅ is in the rangefrom 15.0 μm to 25.0 μm.
 20. The optical fiber of claim 1, wherein thesecondary coating is the cured product of a composition comprising: analkoxylated bisphenol-A diacrylate monomer in an amount greater than 55wt %, the alkoxylated bisphenol-A diacrylate monomer having a degree ofalkoxylation in the range from 2 to 16; and a triacrylate monomer in anamount in the range from 2.0 wt % to 25 wt %, the triacrylate monomercomprising an alkoxylated trimethylolpropane triacrylate monomer havinga degree of alkoxylation in the range from 2 to 16 or atris[(acryloyloxy)alkyl] isocyanurate monomer.
 21. The optical fiber ofclaim 20, wherein the alkoxylated trimethylolpropane triacrylate monomeris an ethoxylated trimethylolpropane triacrylate monomer.
 22. Theoptical fiber of claim 20, wherein the tris[(acryloyloxy)alkyl]isocyanurate monomer is a tris(2-hydroxyethyl) isocyanurate triacrylatemonomer.
 23. The optical fiber of claim 1, wherein the optical fiber hasan effective area at 1550 nm greater than 100 μm².
 24. The optical fiberof claim 1, wherein the optical fiber has a macrobending loss at awavelength of 1550 nm, when wrapped around a mandrel having a diameterof 15 mm, less than 0.5 dB/turn.
 25. The optical fiber of claim 1,wherein the optical fiber has a wire-mesh-covered drum microbending lossat a wavelength of 1550 nm less than 0.5 dB/km.
 26. The optical fiber ofclaim 1, wherein the optical fiber has a wire-mesh-covered drummicrobending loss at a wavelength of 1550 nm less than 0.03 dB/km. 27.The optical fiber of claim 1, wherein the secondary coating has anormalized puncture load greater than 4.5×10⁻³ g/μm².